ARTÍCULO

Taxonomical and nomenclatural notes on Centaurea: A proposal of classification, a description of new sections and subsections, and a species list of the redefined section Centaurea

A. HILPOLD^1,2, N. GARCIA-JACAS¹, R. VILATERSANA¹ & A. SUSANNA¹

¹ Institut Botànic de Barcelona (IBB-CSIC-ICUB), pg. del Migdia, s/n, Parc de Montjuïc, ES-08038 Barcelona, Spain
² Museum of Nature South Tyrol, Bindergasse, 1, IT-39100 Bozen, Italy

Author for correspondence: A. Susanna (asusanna@ibb.csic.es)

Editor: L. Sáez

ABSTRACT
Taxonomical and nomenclatural notes on Centaurea: A proposal of classification, a description of new sections and subsections, and a species list of a redefined section Centaurea.— In this paper, we summarize the results of our long-date research on the genus Centaurea. The first part of the paper deals with the overall classification of the genus, which we propose to divide into three subgenera: subgenus Centaurea, subgenus Cyanus and subgenus Lopholoma. The second part of this publication gives a recopilation of the species of the redefined section Centaurea, a group that includes former sections Acrolophus (sect. Centaurea s. str.), Phalolepis and Willkommia, together with taxonomical, geographical, ecological and karyological considerations. Finally, new descriptions or nomenclatural combinations are proposed to correlate nomenclature to the new classification: a new combination (sect. Acrocentron subsect. Chamaecyanus) is proposed in subgenus Lopholoma; three new sections (sects. Akamantis, Cnicus, and Hyerapolitanae) are described in subgenus Centaurea; two subsections (subsects. Phalolepis and Willkommia) in sect. Centaurea; and three subsections (subsects. Exarata, Jacea, and Subtilis) in sect. Phrygia.
KEYWORDS: Acrocentron; Acrolophus; Akamantis; Chamaecyanus; Cyanus; Exarata; Hierapolitanae; Jacea; Lopholoma; Phalolepis; Phrygia; Subtilis; Willkommia.

Notas taxonómicas y nomenclaturales en Centaurea: propuesta de clasificación, descripción de secciones y subsecciones nuevas, y lista de especies de una sección Centaurea redefinida

RESUMEN
Notas taxonómicas y nomenclaturales en Centaurea: propuesta de clasificación, descripción de secciones y subsecciones nuevas, y lista de especies de una sección Centaurea redefinida.— En este trabajo presentamos los resultados de nuestras investigaciones de larga fecha en el género Centaurea. La primera parte del trabajo trata de la clasificación del género, que proponemos dividir en tres subgéneros: subgénero Centaurea, subgénero Cyanus y subgénero Lopholoma. La segunda parte es una recopilación de las especies de la redefinida sección Centaurea, que incluye las antiguas secciones Acrolophus (sect. Centaurea s. str.), Phalolepis y Willkommia, junto con consideraciones geográficas, ecológicas y cariológicas. Por último, proponemos nuevas secciones, subsecciones y combinaciones para correlacionar nomenclatura y clasificación: proponemos una nueva (sect. Acrocentron subsect. Chamaecyanus) en el subgénero Lopholoma; se describen tres secciones nuevas (sects. Akamantis, Cnicus y Hyerapolitanae) en el subgénero Centaurea; dos subsecciones (subsects. Phalolepis and Willkommia) en la sección Centaurea; y tres subsecciones (subsects. Exarata, Jacea y Subtilis) en la sección Phrygia.
PALABRAS CLAVE: Acrocentron; Acrolophus; Akamantis; Chamaecyanus; Cyanus; Exarata; Hierapolitanae; Jacea; Lopholoma; Phalolepis; Phrygia; Subtilis; Willkommia.

CONTENIDOS

INTRODUCTIONTop

Systematics of Centaurea L. has changed dramatically during the past two decades. Molecular methods have resolved the old problem of the delimitation of the genus (for details see Susanna et al., 1995Susanna, A., Garcia-Jacas, N., Soltis, D. E. & Soltis, P. S. 1995. Phylogenetic relationships in tribe Cardueae (Asteraceae) based on ITS sequences. American Journal of Botany 82: 1056–-1068. ; Garcia-Jacas et al., 2000Garcia-Jacas, N., Susanna, A., Mozaffarian, V. & Ilarslan, R. 2000. The natural delimitation of Centaurea (Asteraceae: Cardueae): ITS sequences analysis of the Jacea group. Plant Systematics and Evolution 223: 185–199. , 2001Garcia-Jacas, N., Susanna, A., Garnatje, T. & Vilatersana, R. 2001. Generic delimitation and phylogeny of the subtribe Centaureinae (Asteraceae): a combined nuclear and chloroplast DNA analysis. Annals of Botany 87: 503–515. , 2006Garcia-Jacas, N., Uysal, T., Romaschenko, K., Suárez-Santiago, V. N., Ertuğrul, K. & Susanna, A. 2006. Centaurea revisited: A molecular survey of the Jacea group. Annals of Botany 98: 741–753. ; Hilpold et al., 2014Hilpold, A., Vilatersana, R., Susanna, A. et al. 2014. Phylogeny of the Centaurea group (Centaurea, Compositae) – geography is a better predictor than morphology. Molecular Phylogenetics and Evolution 77: 195–215.). To put it shortly, Centaurea as defined traditionally (e.g. Linnaeus, 1753Linnaeus, C. 1753. Species plantarum. Impensis Laurentii Salvii, Stockholm.; Bentham, 1873Bentham, G. 1873. Compositae. In: Bentham, G. & Hooker, J. D. (Eds.), Genera Plantarum. Lovell Reeve & Co., London: 162–533. ; Hoffmann, 1894Hoffmann, O. 1894. Compositae. In: Engler, A. & Prantl, K. (Eds.), Die natürlichen pflanzenfamilien. Wilhelm Engelmann, Leipzig: 87–387. ; Dostál, 1976Dostál, J. 1976. Centaurea L. In: Tutin, T. G., Heywood, V. H., Burges, N. A., Moore, D. M., Valentine, D. H., Walters, S. M. & Webb, D. A. (Eds.), Flora Europaea 4. Plantaginaceae to Compositae (and Rubiaceae). Cambridge University Press, Cambridge, London, New York & Melbourne: 254–301. ) was polyphyletic, and molecular studies showed that some clades, including the former section Centaurea (including the type species, Centaurea centaurium L.) had to be excluded in order to make the genus monophyletic. To prevent the renaming of hundreds of species, the type species was changed: the type is now C. paniculata L. (Greuter et al., 2001Greuter, W., Wagenitz, G., Aghababian, M. & Hellwig, F. H. 2001. Proposal to conserve the name Centaurea (Compositae) with a conserved type. Taxon 50: 1201–1205. ). The old section Centaurea acquired the rank of genus on its own, namely Rhaponticoides Vaill. (Greuter, 2003Greuter, W. 2003. The Euro+Med treatment of Cardueae (Compositae) – generic concepts and required new names. Willdenowia 33: 49–61. ; Greuter et al., 2005Greuter, W., Aghababian, M. & Wagenitz, G. 2005. Vaillant on Compositae – systematic concepts and nomenclatural impact. Taxon 54: 149–174. ). However, there are some open questions on the classification of the genus that are discussed in the work here presented.

Centaurea constitutes an important member of tribe Cardueae Cass. (Compositae). It is formed by annual, biennial or perennial herbs, less often shrubs, with usually unarmed leaves (Susanna & Garcia-Jacas, 2007Susanna, A. & Garcia-Jacas, N. 2007. The tribe Cardueae. In: Kadereit, J. W. & Jeffrey, C. (Eds.), Flowering Plants. Eudicots. Asterales. In: Kubitzki, J. (series ed.), The families and genera of vascular plants 8. Springer-Verlag, Heidelberg: 123–146.). They are also characterized by a lateral hilum (Dittrich, 1968Dittrich, M. 1968. Karpologische Untersuchungen zur Systematik von Centaurea und verwandten Gattungen. Teil I. Botanische Jahrbücher für Systematik, Pflanzengeschichte und Pflanzengeographie 88: 70–122, 123–162. ), and a specialized floral morphology with showy sterile peripheral florets without staminodes (Wagenitz & Hellwig, 1996aWagenitz, G. & Hellwig, F. H. 1996a. Evolution of characters and phylogeny of the Centaureinae. In: Hind, D. J. N. & Beentje, H. G. (Eds.), Compositae: Systematics. Proceedings of the International Compositae Conference, Kew, 1994. Royal Botanic Gardens, Kew: 491–510. ). The main morphological character used for systematics within Centaurea is the form of the scarious bract appendages. Centaurea is insect pollinated, mainly by bees and bumblebees (Harrod & Taylor, 1995Harrod, R. J. & Taylor, R. J. 1995. Reproduction and pollination biology of Centaurea and Acroptilon species, with emphasis on C. diffusa. Northwest Science 69: 97–105. ; Bilisik et al., 2008Bilisik, A., Cakmak, I., Bicakci, A. & Malyer, H. 2008. Seasonal variation of collected pollen loads of honeybees (Apis mellifera L. anatolica). Grana 47: 70–77. ; Albrecht et al., 2009Albrecht, M., Duelli, P., Obrist, M. K., Kleijn, D. & Schmid, B. 2009. Effective long-distance pollen dispersal in Centaurea jacea. PLoS One 4: e6751. http://dx.doi.org/10.1371/journal.pone.0006751. ; McIver et al., 2009McIver, J., Thorp, R. & Erickson, K. 2009. Pollinators of the invasive plant yellow starthistle (Centaurea solstitialis) in north-eastern Oregon, USA. Weed Biology and Management 9: 137–145. ). The genus occurs mainly in the Mediterranean and Irano-Turanian regions, with some species (especially from sect. Jacea) extending northwards to temperate Europe. Redefined Centaurea is the largest genus within subtribe Centaureinae encompassing some 250 species (Susanna & Garcia-Jacas, 2007Susanna, A. & Garcia-Jacas, N. 2007. The tribe Cardueae. In: Kadereit, J. W. & Jeffrey, C. (Eds.), Flowering Plants. Eudicots. Asterales. In: Kubitzki, J. (series ed.), The families and genera of vascular plants 8. Springer-Verlag, Heidelberg: 123–146. , 2009Susanna, A. & Garcia-Jacas, N. 2009. The tribe Cardueae. In: Funk, V. A., Susanna, A., Stuessy, T. F. & Bayer, R. J. (Eds.), Systematics, evolution, and biogeography of Compositae. IAPT, Vienna: 293–313. ), but these figures are conservative and somewhat disputed because of wide differences in taxonomical treatments. Besides, the numbers are steedly rising with the description of new species in the Eastern Mediterranean (Aksoy et al., 2008Aksoy, N., Duman, H. & Efe, A. 2008. Centaurea yaltirikii sp. nov. (Asteraceae, C. sect. Pseudoseridia) from Turkey. Nordic Journal of Botany 26: 1756–1051. ).

We published a general outline of a classification of the genus in Susanna & Garcia-Jacas (2007Susanna, A. & Garcia-Jacas, N. 2007. The tribe Cardueae. In: Kadereit, J. W. & Jeffrey, C. (Eds.), Flowering Plants. Eudicots. Asterales. In: Kubitzki, J. (series ed.), The families and genera of vascular plants 8. Springer-Verlag, Heidelberg: 123–146. , 2009Susanna, A. & Garcia-Jacas, N. 2009. The tribe Cardueae. In: Funk, V. A., Susanna, A., Stuessy, T. F. & Bayer, R. J. (Eds.), Systematics, evolution, and biogeography of Compositae. IAPT, Vienna: 293–313. ), but these were general works and we only indicated that we classify Centaurea three subgenera, namely Centaurea, Cyanus (Mill.) Cass. ex Hayek, and Lopholoma (Cass.) Dobrocz. Thereafter, our aims with this paper are: (1) to present an overall classification of the genus, detailing especially our proposal for subgenus Centaurea; (2) to offer a list of species of the newly defined section Centaurea; and (3) to propose some new nomenclatural combinations within subgenera Centaurea and Lopholoma.

MATERIAL AND METHODSTop

For subgenera Cyanus and Lopholoma, our outline is based on the studies by Boršić et al. (2011Boršić, I., Susanna, A., Bancheva, S. & Garcia-Jacas, N. 2011. Centaurea sect. Cyanus: nuclear phylogeny, biogeography, and life-form evolution. International Journal of Plant Sciences 172: 238–249. ) and Font et al. (2002Font, M., Garnatje, T., Garcia-Jacas, N. & Susanna, A. 2002. Delineation and phylogeny of Centaurea sect. Acrocentron based on DNA sequences: a restoration of the genus Crocodylium and indirect evidence of introgression. Plant Systematics and Evolution 234: 15–26. , 2009Font, M., Garcia-Jacas, N., Vilatersana, R., Roquet, C. & Susanna, A. 2009. Evolution and biogeography of Centaurea section Acrocentron inferred from nuclear and plastid DNA sequence analyses. Annals of Botany 103: 985–997. ), respectively. Regarding subg. Centaurea, our proposal follows the layout suggested by Garcia-Jacas et al. (2006Garcia-Jacas, N., Uysal, T., Romaschenko, K., Suárez-Santiago, V. N., Ertuğrul, K. & Susanna, A. 2006. Centaurea revisited: A molecular survey of the Jacea group. Annals of Botany 98: 741–753. ) and Hilpold (2012Hilpold, A. 2012. Evolution of the Centaurea Acrolophus subgroup. PhD Thesis, University of Barcelona, Barcelona. ), and is partly provisional for the Eastern Mediterranean (EMC) and Western Mediterranean (WMC) clades, which are in need of a more complete molecular survey.

As regards to the list of species of sect. Centaurea, we have followed current literature, basically floras. Taxonomy follows Euro+Med Plantbase (Euro+Med, 2006–2013Euro+Med. 2006–2013. Euro+Med Plantabase – The information resource for Euro-Mediterranean plan diversity. Compositae. Retrieved November, 2013, from http://ww2.bgbm.org/EuroPlusMed/.) for the Eastern and Central Mediterranean region, and López & Devesa (2008aLópez, E. & Devesa, J. A. 2008a. Notas taxonómicas sobre el género Centaurea L. (Asteraceae) en la Península Ibérica. II. C. castellanoides Talavera y C. aristata Hoffmanns. & Link. Acta Botanica Malacitana 33: 57–68. , 2008bLópez, E. & Devesa, J. A. 2008b. Notas taxonómicas sobre el género Centaurea L. (Asteraceae) en la Península Iberica. III. Centaurea limbata Hoffmanns. & Link. Lagascalia 28: 411–423. , 2008cLópez, E. & Devesa, J. A. 2008c. Notas taxonómicas sobre el género Centaurea L. (Asteraceae) en la Península Ibérica. I. C. cordubensis Font Quer, C. bethurica E. López & Devesa, sp. nov., y C. schousboei Lange. Anales del Jardin Botánico de Madrid 65: 331–341. , 2008dLópez, E. & Devesa, J. A. 2008d. Contribución al conocimiento cariológico del género Centaurea L. (Asteraceae) en la Península Ibérica. Acta Botanica Malacitana 33: 69–90. , 2010López, E. & Devesa, J. A. 2010. Notas taxonómicas sobre el género Centaurea (Asteraceae) en la Península Ibérica. C. paniculata, C. hanryi y C. diffusa. Anales del Jardin Botánico de Madrid 67: 113–126. , 2011López, E. & Devesa, J. A. 2011. Revisión taxonómica del complejo Centaurea alba L. (Asteraceae) en la Península Ibérica. Collectanea Botanica (Barcelona) 30: 37–52. ) and López et al., (2011López, E., Devesa, J. A. & Arnelas, I. 2011. Taxonomic study in the Centaurea langei complex. Annales Botanici Fennici 48: 1–12. ) for the Iberian Peninsula. More details on the construction of the Table 2 are given below.

DISCUSSION AND CONCLUSIONSTop

On the light of our previous results, we summarize our proposal of a classification for the genus (new sections, subsections and nomenclatural combinations are formally proposed at the end of the article):

Centaurea L.

Subgenus Lopholoma (Cass.) Dobrocz.

Sect. Acrocentron (Cass.) DC.

Subsect. Acrocentron

Subsect. Chamaecyanus (Willk.) new status and combination

Sect. Stephanochilus (Coss. & Durieu ex Benth. & Hook. f.) O. Hoffm.

Subgenus Cyanus (Mill.) Cass. ex Hayek

Sect. Cyanus

Subsect. Cyanus

Subsect. Perennes Boiss.

Subgenus Centaurea

Eastern Mediterranean Clade (EMC)

Sect. Calcitrapa DC. [incl. sects. Seridioides DC. and sect. Tetramorphaea (DC.) Boiss.]

Sect. Chartolepis (Cass.) DC.

Sect. Cheirolepis (Boiss.) O. Hoffm. [incl. sect. Plumosipappus (Czerep.) Wagenitz, sect. Pseudoseridia Wagenitz p. p. and sect. Pteracantha Wagenitz]

Sect. Cynaroides Boiss. ex Walp. [incl. sect. Paraphysis (DC.) Wagenitz]

Sect. Grossheimia (Sosn. & Takht.) Dittrich

Sect. Microlophus (Cass.) DC.

Sect. Phaeopappus (DC.) O. Hoffm.

Sect. Pseudophaeopappus Wagenitz

Sect. Ptosimopappus (Boiss.) O. Hoffm.

Sect. Rhizocalathium Tzvelev (incl. sect. Pseudoseridia Wagenitz p. p.)

Western Mediterranean Clade (WMC)

Sect. Hymenocentron (Cass.) DC.

Sect. Melanoloma (Cass.) DC. (incl. sect. Gymnocyanus Maire)

Sect. Mesocentron (Cass.) DC.

Sect. Seridia (Juss.) DC.

Circum-Mediterranean Clade (CMC)

Sect. Centaurea

Subsect. Centaurea

Subsect. Phalolepis (Cass.) new combination

Subsect. Willkommia (Blanca) new combination

Sect. Akamantis new section

Sect. Ammocyanus Boiss.

Sect. Cnicus (L.) new status and combination

Sect. Hierapolitanae new section

Sect. Phrygia Pers.

Subsect. Phrygia

Subsect. Exarata, new subsection

Subsect. Jacea (L.) new status and combination

Subsect. Subtilis, new subsection

The genus Centaurea contains three well delimited subgenera: Lopholoma (often named Acrocentron), Cyanus and Centaurea (the latter corresponds to the Jacea group sensu Garcia-Jacas et al., 2006Garcia-Jacas, N., Uysal, T., Romaschenko, K., Suárez-Santiago, V. N., Ertuğrul, K. & Susanna, A. 2006. Centaurea revisited: A molecular survey of the Jacea group. Annals of Botany 98: 741–753. ). Cyanus has been also treated as separate genus (e.g. Greuter, 2003Greuter, W. 2003. The Euro+Med treatment of Cardueae (Compositae) – generic concepts and required new names. Willdenowia 33: 49–61. ). We suggest treating them in the rank of subgenera. These three subgenera are well separated on the basis of molecular markers (Garcia-Jacas et al., 2001Garcia-Jacas, N., Susanna, A., Garnatje, T. & Vilatersana, R. 2001. Generic delimitation and phylogeny of the subtribe Centaureinae (Asteraceae): a combined nuclear and chloroplast DNA analysis. Annals of Botany 87: 503–515. ; Susanna et al., 2006Susanna, A., Garcia-Jacas, N., Hidalgo, O., Vilatersana, R. & Garnatje, T. 2006. The Cardueae (Compositae) revisited: Insights from ITS, trnL-trnF, and matK nuclear and chloroplast DNA analysis. Annals of the Missouri Botanical Garden 93: 150–171. ; Barres et al., 2013Barres, L., Sanmartín, I., Anderson, C.-L., Susanna, A., Buerki, S., Galbany-Casals, M. & Vilatersana, R. 2013. Reconstructing the evolution and biogeographic history of tribe Cardueae (Compositae). American Journal of Botany 100: 867–882. ) and correspond to the existing pollen types.

The pollen of the genus Centaurea is, like that of all Compositae (Blackmore et al., 2009Blackmore, S., Wortley, A. H., Skvarla, J. J. & Robinson, H. 2009. Evolution of pollen in Compositae. In: Funk, V. A., Susanna, A., Stuessy, T. F. & Bayer, R. J. (Eds.), Systematics, evolution, and biogeography of Compositae. IAPT, Vienna: 101–130. ), tricolporate and the ectexine is formed by two layers of columellae (Wagenitz, 1955Wagenitz, G. 1955. Pollenmorphologie und Systematik in der Gattung Centaurea L. s. l. Flora 142: 213–279. ). Within the genus, four clearly distinct pollen types can be found, which correspond to the three subgenera (Wagenitz, 1955Wagenitz, G. 1955. Pollenmorphologie und Systematik in der Gattung Centaurea L. s. l. Flora 142: 213–279. ; Martín & Garcia-Jacas, 2000 Martín, J. & Garcia-Jacas, N. 2000. Pollen studies in subtribe Centaureinae (Asteraceae): the Jacea group analysed with electron microscopy. Botanical Journal of the Linnean Society 133: 473–484. ; Susanna & Garcia-Jacas, 2009Susanna, A. & Garcia-Jacas, N. 2009. The tribe Cardueae. In: Funk, V. A., Susanna, A., Stuessy, T. F. & Bayer, R. J. (Eds.), Systematics, evolution, and biogeography of Compositae. IAPT, Vienna: 293–313. ). Centaureinae show a dysploid chromosome series, with basic chromosome numbers ranging between x = 16 and x = 7 (Garcia-Jacas et al., 1996Garcia-Jacas, N., Susanna, A. & Ilarslan, R. 1996. Aneuploidy in the Centaureineae (Compositae): Is n = 7 the end of the series? Taxon 45: 39–42. ). Low numbers can be found in more evolved groups and have been interpreted as an adaptation to dry conditions (Susanna & Garcia-Jacas, 2009Susanna, A. & Garcia-Jacas, N. 2009. The tribe Cardueae. In: Funk, V. A., Susanna, A., Stuessy, T. F. & Bayer, R. J. (Eds.), Systematics, evolution, and biogeography of Compositae. IAPT, Vienna: 293–313. ). Chromosome numbers in Centaurea range from x = 12 to x = 7 (Table 1). Whereas subgenera Cyanus and Centaurea have a broad range of chromosome numbers, subgenus Lopholoma is more conservative, showing only two chromosome numbers. Chromosome numbers in the EMC and in the WMC follow largely the sectional division. The lowest chromosome number known to date in the genus was found in the annual Centaurea patula DC. with x = 7.

Centaurea is rich in secondary metabolites, which may mostly be a protection against herbivores (Olson & Kelsey, 1997Olson, B. E. & Kelsey, R. G. 1997. Effect of Centaurea maculosa on sheep rumen microbial activity and mass in vitro. Journal of Chemical Ecology 23: 1131–1144. ; Susanna & Garcia-Jacas, 2009Susanna, A. & Garcia-Jacas, N. 2009. The tribe Cardueae. In: Funk, V. A., Susanna, A., Stuessy, T. F. & Bayer, R. J. (Eds.), Systematics, evolution, and biogeography of Compositae. IAPT, Vienna: 293–313. ). Some of them show antimicrobial activity (Karioti et al., 2001Karioti, A., Skaltsa, H., Lazari, D., Sokovic, M., Garcia, B. & Harvala, C. 2001. Secondary metabolites from Centaurea deusta with antimicrobial activity. Zeitschrift für Naturforschung 57: 75–80. ; Ugur et al., 2009Ugur, A., Sarac, N., Ceylan, O. & Duru, M. E. 2009. Chemical composition of endemic Centaurea austro-anatolica and studies of its antimicrobial activity against multi-resistant bacteria. Acta Pharmaceutica 58: 463–472. ). Metabolites are predominantly sesquiterpene lactones (Tarasov et al., 1975Tarasov, V. A., Kasymov, S. Z. & Sidyakin, G. P. 1975. The isolation of Cnicin from Centaurea squarrosa. Chemistry of Natural Compounds 9: 414. ; Koukoulitsa et al., 2005Koukoulitsa, C., Geromichalos, G. D. & Skaltsa, H. 2005. VolSurf analysis of pharmacokinetic properties for several antifungal sesquiterpene lactones isolated from Greek Centaurea sp. Journal of Computer-Aided Molecular Design 19: 617–623. ; Karamenderes et al., 2007Karamenderes, C., Bedir, E., Abou-Gazar, A. & Khan, I. A. 2007. Chemical constituents of Centaurea cadmea. Chemistry of Natural Compounds 43: 694–695. ), but also flavonoids (Zapesochnaya et al., 1978Zapesochnaya, G. G., Evstratova, R. I. & Mukhametzhanov, M. N. 1978. Methoxyflavones of some species of Centaurea. Chemistry of Natural Compounds 13: 590–591. ; Nacer et al., 2006Nacer, A., Bernard, A., Boustie, J., Touzani, R. & Kabouche, Z. 2006. Aglycone flavonoids of Centaurea tougourensis from Algeria. Chemistry of Natural Compounds 42: 230. ), essential oils (Altintas et al., 2004Altintas, A, Köse, Y. B., Yucel, E., Demirci, B. & Baser, K. H. C. 2004. Composition of the essential oil of Centaurea dichroa. Chemistry of Natural Compounds 40: 604. ) and phenols (Bubenchikov et al., 1992Bubenchikov, V. N., Kitvinenko, V. I. & Popova, T. P. 1992. Phenolic compounds of Centaurea pseudomaculosa. Chemistry of Natural Compounds 28: 507. ). Many phytochemical studies have been published over the last decade but only very few address explicitly systematic questions (but see Yildirim et al., 2009).

Subgenus Lopholoma

This subgenus comprises about 100 species (Font et al., 2002Font, M., Garnatje, T., Garcia-Jacas, N. & Susanna, A. 2002. Delineation and phylogeny of Centaurea sect. Acrocentron based on DNA sequences: a restoration of the genus Crocodylium and indirect evidence of introgression. Plant Systematics and Evolution 234: 15–26. ) and is distributed all over the Mediterranean with one species, Centaurea scabiosa L., reaching the high north of Europe. The flower heads of Lopholoma are usually larger than in the other subgenera, and the bract appendages often ends in a long spine (Fig. 1A). The group is also morphologically well differentiated by presenting an only and characteristic pollen type, the Centaurea scabiosa type (Wagenitz, 1955Wagenitz, G. 1955. Pollenmorphologie und Systematik in der Gattung Centaurea L. s. l. Flora 142: 213–279. ). This subgenus was studied applying molecular tools by Font et al. (2002Font, M., Garnatje, T., Garcia-Jacas, N. & Susanna, A. 2002. Delineation and phylogeny of Centaurea sect. Acrocentron based on DNA sequences: a restoration of the genus Crocodylium and indirect evidence of introgression. Plant Systematics and Evolution 234: 15–26. , 2009Font, M., Garcia-Jacas, N., Vilatersana, R., Roquet, C. & Susanna, A. 2009. Evolution and biogeography of Centaurea section Acrocentron inferred from nuclear and plastid DNA sequence analyses. Annals of Botany 103: 985–997. ). There are two groups within the subgenus that should be treated as two different sections: The former monotypic genus Stephanochilus Coss. & Dur. ex Benth. is sister to all other members of the subgenus (Font et al., 2002Font, M., Garnatje, T., Garcia-Jacas, N. & Susanna, A. 2002. Delineation and phylogeny of Centaurea sect. Acrocentron based on DNA sequences: a restoration of the genus Crocodylium and indirect evidence of introgression. Plant Systematics and Evolution 234: 15–26. ) and constitutes the first section. The second section, section Acrocentron, encompasses all other species of the subgenus. On molecular basis, Font et al. (2009Font, M., Garcia-Jacas, N., Vilatersana, R., Roquet, C. & Susanna, A. 2009. Evolution and biogeography of Centaurea section Acrocentron inferred from nuclear and plastid DNA sequence analyses. Annals of Botany 103: 985–997. ) suggested that sect. Chamaecyanus Willk. is not clearly distinguishable from sect. Acrocentron despite clear morphological differences (a very short and simplified pappus combined with acaulescent habit). We propose to merge Chamaecyanus as subsection in section Acrocentron.

Subgenus Cyanus

The subgenus stands out by its predominantly bright blue flowers, as shown by its most prominent member, the cornflower (Centaurea cyanus L.; Fig. 1B). Further characters for this subgenus are two pollen types (Cyanus and Montana types of Wagenitz, 1955) and the pectinate-ciliate, unarmed, decurrent appendages of the phyllaries (Wagenitz & Hellwig, 1996a). The subgenus comprises about 40 species, also concentrated in the Mediterranean, reaching central Asia and the Caucasus. Molecular studies of the group were carried out by Boršić et al. (2011Boršić, I., Susanna, A., Bancheva, S. & Garcia-Jacas, N. 2011. Centaurea sect. Cyanus: nuclear phylogeny, biogeography, and life-form evolution. International Journal of Plant Sciences 172: 238–249. ), Olšavská et al. (2011Olšavská, K., Perný, M., Kućera, J. & Hodálová, I. 2011. Biosystematic study of the Cyanus triumfetti group in Central Europe. Preslia 83: 59–98. ) and Löser (2013Löser, C. J. 2013. Speciation and genomic conflicts in Cyanus Mill. PhD Thesis, University of Jena, Jena. ). The study of Boršić et al. (2011Boršić, I., Susanna, A., Bancheva, S. & Garcia-Jacas, N. 2011. Centaurea sect. Cyanus: nuclear phylogeny, biogeography, and life-form evolution. International Journal of Plant Sciences 172: 238–249. ) confirmed the existence of two clearly distinct clades already marked by the pollen types and life cycles, corresponding to subsects. Cyanus (annuals) and Perennes (perennials).

Figure 1. Photographs of the genus Centaurea, with special emphasis on subgenus Centaurea and sect. Centaurea. (A), Subgen. Lopholoma: C. ornata, Soria, Spain (Photograph: A. Susanna); (B), Subgen. Cyanus: Centaurea cyanus, Soria, Spain (Photograph: A. Susanna). (C) Subgen. Centaurea: East-Mediterranean Clade (EMC): (C), C. lycopifolia, Barcelona Botanical Garden (Photograph: A. Susanna). (D–N), Circum-Mediterranean Clade (CMC). (D), C. benedicta, Barcelona Botanical Garden (Photograph: A. Susanna); (E), C. akamantis, Avakas gorge, Cyprus (Photograph: M. Galbany); (F), C. hierapolitana, Afon lake, Turkey (Photograph: A. Susanna); (G), C. hyrcanica (Jacea-Phrygia group), Iran (Photograph: A. Pirani); (H), C. exarata, Barcelona Botanical Garden (Photograph: A. Susanna); (I), C. patula, Barcelona Botanical Garden (Photograph: A. Susanna). (J–N), Sect. Centaurea. (J), C. tenorei, Minori, Italy (Photograph: A. Hilpold); (K), C. alba, Sierra de Aracena, Spain (Photograph: L. Barres); (L), C. pulvinata, Sierra de Abrucena, Spain (Photograph: G. Blanca); (M), C. horrida, Sardinia (Photograph: S. Pisanu); (N), C. princeps, Barcelona Botanical Garden (Photograph: A. Susanna); (O), C. panormitana, Sferracavallo, Sicily (Photograph: A. Hilpold). [View full size] [Descargar tamaño completo]

Subgenus Centaurea

This subgenus corresponds to the Jacea group sensu Garcia-Jacas et al. (2006Garcia-Jacas, N., Uysal, T., Romaschenko, K., Suárez-Santiago, V. N., Ertuğrul, K. & Susanna, A. 2006. Centaurea revisited: A molecular survey of the Jacea group. Annals of Botany 98: 741–753. ) and it is the most species-rich. It is represented by several hundreds of species mainly in the Mediterranean Region but also in Western Asia and Central and Eastern Europe. The most characteristic trait of the subgenus is the pollen type, the so-called Jacea pollen type (Wagenitz, 1955Wagenitz, G. 1955. Pollenmorphologie und Systematik in der Gattung Centaurea L. s. l. Flora 142: 213–279. ; Garcia-Jacas et al., 2000Garcia-Jacas, N., Susanna, A., Mozaffarian, V. & Ilarslan, R. 2000. The natural delimitation of Centaurea (Asteraceae: Cardueae): ITS sequences analysis of the Jacea group. Plant Systematics and Evolution 223: 185–199. ). New systematic insights of the subgenus on molecular grounds were provided by Garcia-Jacas et al. (2006Garcia-Jacas, N., Uysal, T., Romaschenko, K., Suárez-Santiago, V. N., Ertuğrul, K. & Susanna, A. 2006. Centaurea revisited: A molecular survey of the Jacea group. Annals of Botany 98: 741–753. ). One of the main results of this study, based on ITS sequence analyses, was the separation of subgen. Centaurea into three clades, which where named after their main geographic distribution: the Eastern Mediterranean Clade (EMC) comprises species often with spiny bract appendages from the Eastern Mediterranean (Fig. 1C shows C. lycopifolia Boiss. & Kotschy ex Boiss.), including the widely distributed weed Centaurea calcitrapa L.; the Western Mediterranean Clade (WMC), the members of which also show pronounced spiny bract appendages, well visible in the common weeds Centaurea solstitialis L. or C. sulphurea Willd.; and the Circum-Mediterranean Clade (CMC), the members of which are predominantly not or only slightly spiny in their bract appendages. Despite their wide distribution, their importance as weeds, and the high species diversity, our knowledge about systematics within the EMC and the WMC is poor and would need a more comprehensive study with molecular methods. The CMC, however, was already the centre of attention of profound molecular work (see below).

The most distinctive characters of the CMC are also the bract appendages (Fig. 1D–N). There are three extreme forms: membranaceous, long ciliate-fimbriate, and reduced or missing appendages. According to Garcia-Jacas et al. (2006Garcia-Jacas, N., Uysal, T., Romaschenko, K., Suárez-Santiago, V. N., Ertuğrul, K. & Susanna, A. 2006. Centaurea revisited: A molecular survey of the Jacea group. Annals of Botany 98: 741–753. ) most species within the CMC belong to two main clades: the Jacea-Phrygia group (hereafter referred to as section Phrygia) and the Centaurea group (formerly Acrolophus subgroup; hereafter referred to as section Centaurea; Wagenitz & Hellwig, 1996aWagenitz, G. & Hellwig, F. H. 1996a. Evolution of characters and phylogeny of the Centaureinae. In: Hind, D. J. N. & Beentje, H. G. (Eds.), Compositae: Systematics. Proceedings of the International Compositae Conference, Kew, 1994. Royal Botanic Gardens, Kew: 491–510. ). Following Hilpold (2012Hilpold, A. 2012. Evolution of the Centaurea Acrolophus subgroup. PhD Thesis, University of Barcelona, Barcelona. ), besides these two groups, four more sections belong to the CMC: the new monotypic section Akamantis consisting of Centaurea akamantis T. Georgiadis & Hadjik. from Cyprus, section Ammocyanus composed of C. ammocyanus Boiss. and C. patula, the new monotypic section Cnicus consisting of Centaurea benedicta (L.) L. (formerly Cnicus benedictus L.) and the new section Hierapolitanae, including C. hierapolitana Boiss. and C. tossiensis Freyn & Sint. ex Freyn from Turkey.

Section Phrygia — Members of section Phrygia can be distinguished from those of section Centaurea by (1) the basic chromosome numbers, x = 11 vs. x = 9 respectively, (2) the leaf shape, since Phrygia leaves are entire, while in section Centaurea at least the basalmost leaves are deeply divided. Section Phrygia also has a different ecology and distribution: species of sect. Centaurea are much more dry adapted and bound to Mediterranean climate, whereas the vast majority of species of sect. Phrygia are typical elements of montane and subalpine meadows, influenced by frequent mowing, grazing or avalanches. They are dependent on a good and constant water supply and are quite resistant to cold periods. These adaptations permitted the group also to disperse into the high north of Europe, with species like Centaurea nigra L. or C. jacea L. Taxonomy within sect. Phrygia is highly complex, and the latest attempts to elucidate it using molecular markers (Koutecký et al., 2011Koutecký, P., Badurová, T., Štech, M., Košnar, J. & Karásek, J. 2011. Hybridization between diploid Centaurea pseudophrygia and tetraploid C. jacea (Asteraceae): the role of mixed pollination, unreduced gametes, and mentor effects. Biological Journal of the Linnean Society 104: 93–106. ; López-Alvarado, 2012López-Alvarado, J. 2012. Centaurea L. section Phrygia Pers.: Phylogeny and biogeography. PhD Thesis, University of Sassari, Sassari.) are only partially satisfying because of the very low levels of variation found. The apparent lack of any intrinsic breeding barriers led to the description of many hybrids on one hand (Vanderhoeven et al., 2002Vanderhoeven, S., Hardy, O., Vekemans, X., Lefèbre, C., De Loose, M., Lambinon, J. & Meerts, P. 2002. A morphometric study of populations of the Centaurea jacea complex (Asteraceae) in Belgium. Plant Biology 4: 403–412. ; Koutecký et al., 2011Koutecký, P., Badurová, T., Štech, M., Košnar, J. & Karásek, J. 2011. Hybridization between diploid Centaurea pseudophrygia and tetraploid C. jacea (Asteraceae): the role of mixed pollination, unreduced gametes, and mentor effects. Biological Journal of the Linnean Society 104: 93–106. ; Vonica & Cantor, 2011Vonica, G. & Cantor, M. 2011. The polymorphism and hybridization of the Centaurea species. Bulletin UASVM Horticulture 68: 444–450. ). On the other hand, a split of the breeding communities into diploid and tetraploid lineages, connected by frequent polyploidization events, was observed (Hardy et al., 2000Hardy, O. J., Vanderhoeven, S., De Loose, M. & Meerts, P. 2000. Ecological, morphological and allozymic differentiation between diploid and tetraploid knapweeds (Centaurea jacea) from a contact zone in the Belgian Ardennes. New Phytologist 146: 281–290. ; Koutecký, 2007Koutecký, P. 2007. Morphological and ploidy level variation of Centaurea phrygia agg. (Asteraceae) in the Czech Republic, Slovakia and Ukraine. Folia Geobotanica 42: 77–102. ; Koutecký et al., 2011Koutecký, P., Badurová, T., Štech, M., Košnar, J. & Karásek, J. 2011. Hybridization between diploid Centaurea pseudophrygia and tetraploid C. jacea (Asteraceae): the role of mixed pollination, unreduced gametes, and mentor effects. Biological Journal of the Linnean Society 104: 93–106. ). Traditional systematics based on morphology within this group uses merely the shape of the bract appendages for the subdivision into two groups: Phrygia (formerly Lepteranthus) with long, fimbriate bract appendages and Jacea with either short ciliate or membranaceous bract appendages. Intermediate forms between these extremes are commonly attributed to hybridization events (Vanderhoeven et al., 2002 Vanderhoeven, S., Hardy, O., Vekemans, X., Lefèbre, C., De Loose, M., Lambinon, J. & Meerts, P. 2002. A morphometric study of populations of the Centaurea jacea complex (Asteraceae) in Belgium. Plant Biology 4: 403–412. ; Koutecký, 2007Koutecký, P. 2007. Morphological and ploidy level variation of Centaurea phrygia agg. (Asteraceae) in the Czech Republic, Slovakia and Ukraine. Folia Geobotanica 42: 77–102. ; Vonica & Cantor, 2011Vonica, G. & Cantor, M. 2011. The polymorphism and hybridization of the Centaurea species. Bulletin UASVM Horticulture 68: 444–450. ). We suggest keeping these two groups the rank of subsections.

Section Centaurea — The type section has its centre of distribution around the Mediterranean and the Black Sea (Fig. 2). Highest species numbers can be found in the Balkan Peninsula, Italy, Turkey and the Iberian Peninsula (in order of abundance). Almost all African species are concentrated in the NW of the continent, in the Atlas mountain ranges. A few widespread species reach central Europe and the Baltic Sea (C. stoebe L.) and Middle Asia, Afghanistan and Pakistan (C. virgata Lam.).

Figure 2. Distribution of sect. Centaurea (without introduced populations). Dark grey: areas with more than one species occurring. Light grey: only one species occurring, species name is given. Numbers show the approximate species number in the area. Note that the species numbers reflect, besides real differences in diversity, also the species concepts used in the different areas. [View full size] [Descargar tamaño completo]

All members of sect. Centaurea grow in dry, open vegetation. Many species can be found in frequently pastured garrigues, on the coast or in the interior. Furthermore, open rocks are inhabited. Only exceptionally, high mountain areas were colonized. Some species are specialized in sandy beaches (e.g. C. spinosa L.). Both substrates, calcareous and siliceous soils are inhabited with predominance on the first ones. Members of sect. Centaurea are rarely selfing or even obligate outcrossers (Harrod & Taylor, 1995Harrod, R. J. & Taylor, R. J. 1995. Reproduction and pollination biology of Centaurea and Acroptilon species, with emphasis on C. diffusa. Northwest Science 69: 97–105. ; Hardy et al., 2004). Reproduction is usually sexual (Noyes, 2007Noyes, R. D. 2007. Apomixis in the Asteraceae: Diamonds in the rough. Functional Plant Science and Biotechnology 1: 207–222. ), although facultative apospory has been reported (Cela Renzoni & Viegi, 1982Cela Renzoni, G. & Viegi, L. 1982. Centaurea cineraria s. l. (Asteraceae) in Italia: Revisione citotassonomica. Atti della Società Toscana di Scienze Naturali di Pisa, Memorie, Serie B 39: 99–144. ).

Species of sect. Centaurea have a basic chromosome number of x = 9. Most counted populations are diploid (2n = 18; Fig. 3). Tetraploids (2n = 36) are frequent, and they have been subject of recent scientific work (Španiel et al., 2008Španiel, S., Marhold, K., Hodálová, I. & Lihová, J. 2008. Diploid and tetraploid cytotypes of Centaurea stoebe (Asteraceae) in Central Europe: morphological differentiation and cytotype distribution patterns. Folia Geobotanica 43: 131–158. ; Mráz et al., 2012Mráz, P., Garcia-Jacas, N., Gex-Fabry, E., Susanna, A., Barres, L. & Müller-Schärer, H. 2012. Allopolyploid origin of highly invasive Centaurea stoebe s. l. (Asteraceae). Molecular Phylogenetics and Evolution 62: 612–623. ). Three species are hexaploid (2n = 6x = 54): C. carystea Trigas & Constantin., C. cithaeronea Phitos & Constantin. and C. tuzgoluensis Aytaç & H. Duman; cf. Phitos & Constantinidis, 1993Phitos, D. & Constantinidis, T. 1993. A new species of Centaurea sect. Phalolepis from Greece. Flora Mediterranea 3: 273–275. ; Martın et al., 2009Martın, E., Dinç, M. & Duran, A. 2009. Karyomorphological study of eight Centaurea L. taxa (Asteraceae) from Turkey. Turkish Journal of Botany 33: 97–104. ; Trigas et al. 2008Trigas, P., Constantinidis, T. & Touloumenidou, T. 2008. A new hexaploid species of Centaurea section Acrolophus (Asteraceae) from Evvia Island, Greece. Botanical Journal of the Linnean Society 158: 762–774. , respectively. Two species with divergent chromosome numbers (x = 11), Centaurea exarata Boiss. ex Coss. and C. subtilis Bertol., traditionally assigned to sect. Centaurea, were found to be closely related to the Centaurea jacea complex (sect. Phrygia) and thereafter were removed from sect. Centaurea (Garcia-Jacas et al., 2006Garcia-Jacas, N., Uysal, T., Romaschenko, K., Suárez-Santiago, V. N., Ertuğrul, K. & Susanna, A. 2006. Centaurea revisited: A molecular survey of the Jacea group. Annals of Botany 98: 741–753. ; Hilpold et al., 2009Hilpold, A., Garcia-Jacas, N., Vilatersana, R. & Susanna, A. 2009. Two additions to the Jacea-Lepteranthus complex: Parallel adaptation in the enigmatic species Centaurea subtilis and C. exarata. Collectanea Botanica (Barcelona) 28: 47–58. ). Counts of chromosome numbers differing from the basic number x = 9 are extremely rare: 2n = 44 (one single count by Baden (1983) in C. affinis Friv., usually with x = 9), 2n = 16 (in C. deustiformis Adamović; Strid, 1983Strid, A. 1983. In: Löve, A. (Ed.), IOPB chromosome number reports 78. Taxon 32: 138–140. ; only in one out of many counts in C. diffusa Lam.; Bancheva & Greilhuber, 2006Bancheva, S. & Greilhuber, J. 2006. Genome size in Bulgarian Centaurea s. l. (Asteraceae). Plant Systematics and Evolution 257: 95–117. ), and 2n = 32 (in C. arenaria Willd.; Bancheva & Greilhuber, 2006Bancheva, S. & Greilhuber, J. 2006. Genome size in Bulgarian Centaurea s. l. (Asteraceae). Plant Systematics and Evolution 257: 95–117. ). Figure 3 shows the percentages of counted species and the distribution of the known chromosome numbers.

Figure 3. Pie diagram indicating the percentages of known - unknown chromosome numbers a, ploidy levels, and discording results in Centaurea sect. Centaurea. [View full size] [Descargar tamaño completo]

A few members of sect. Centaurea are used as ornamentals, like Centaurea cineraria L. (“Velvet Centaurea”, cf. Ellis, 1999Ellis, B. W. 1999. Taylor’s guide to annuals – How to select and grow more than 400 annuals, biennials, and tender perennials. Haughton Mifflin, New York. ). Some species are used as medicinals, especially in folk medicine, because of its secondary compounds (Nacer et al., 2006Nacer, A., Bernard, A., Boustie, J., Touzani, R. & Kabouche, Z. 2006. Aglycone flavonoids of Centaurea tougourensis from Algeria. Chemistry of Natural Compounds 42: 230. ; Akkol et al., 2009Akkol, E. K., Arifa, R., Fatma, E. F. & Yesilada, E. 2009. Sesquiterpene lactones with antinociceptive and antipyretic activity from two Centaurea species. Journal of Ethnopharmacology 122: 210–215. ). The sesquiterpene lactone cnicin, found in Centaurea benedicta (the name of the compound derives from its former name Cnicus benedictus L.) and other species of sect. Centaurea (Olson et al., 1997Olson, B. E. & Kelsey, R. G. 1997. Effect of Centaurea maculosa on sheep rumen microbial activity and mass in vitro. Journal of Chemical Ecology 23: 1131–1144. ; Erel et al., 2011Erel, S. B., Karaalp, C., Bedir, E., Kaehlig, H., Glasl, S., Khan, S. & Krenn, L. 2011. Secondary metabolites of Centaurea calolepis and evaluation of cnicin for anti-inflammatory, antioxidant, and cytotoxic activities. Pharmaceutical Botany 49: 840–849. ) is sometimes used for bitter tonics (Tešević et al., 2007Tešević, V., Milosavljević, S., Vajs, V., Janaćković, P., Đjordjević, I., Jadranin, M. & Vuďović, I. 2007. Quantitative analysis of sesquiterpene lactone cnicin in seven Centaurea species wild-growing in Serbia and Montenegro using H-NMR spectroscopy. Journal of the Serbian Chemical Society 72: 1275–1280. ).

Most important, however, are not the benefits that members of sect. Centaurea provide, but their negative impacts on agriculture and landscape. Centaurea stoebe (= C. maculosa Lam.) and to a lesser extent C. diffusa and C. virgata subsp. squarrosa (Boiss.) Gugler, are tremendous invasive weeds in pastures of the US and Canada. Centaurea stoebe, “one of North America’s most devastating invasive plants” (Blair & Hufbauer, 2010Blair, A. C. & Hufbauer, R. A. 2010. Hybridization and invasion: one of North America’s most devastating invasive plants shows evidence for a history of interspecific hybridization. Evolutionary Applications 3: 40–51. ), diminishes the fodder value of pastures infesting about 3 million ha (Di Tomaso, 2000Di Tomaso, J. M. 2000. Invasive weeds in rangelands: Species, impacts, and management. Weed Science 48: 255–265. ) producing in this way economic damage of hundreds of million dollars every year. The estimated damage for the agriculture of Montana amounts to 42 million dollars (Duncan et al., 2001Duncan, C., Story, J. & Sheley, R. L. 2001. Montana’s knapweeds: Identification, biology and management. Montana State University Extension Service, Bozeman. Retrieved March, 2014, from http://www.sheepinstitute.montana.edu/articles/eb311.html. ). The fight against these weeds is also the motor of most of the research conducted in Centaurea (e.g. Hufbauer & Sforza, 2008Hufbauer, R. A. & Sforza, R. 2008. Multiple introductions of two invasive Centaurea taxa into North America. Diversity and Distributions 14: 252–261. ; Collins et al., 2011Collins, A. R., Ruhollah, N. & Müller-Schärer, H. 2011. Competition between cytotypes changes across a longitudinal gradient in Centaurea stoebe (Asteraceae). American Journal of Botany 98: 1935–1942. ; Pollock et al., 2011Pollock, J. L., Kogan, L. A., Thorpe, A. S. & Holben, W. E. 2011. (+/-)–catechin, a root exudate of the invasive Centaurea stoebe Lam. (spotted knapweed) exhibits bacteriostatic activity against multiple soil bacterial populations. Journal of Chemical Ecology 37: 1044–1053. ; Reinhart & Rinella, 2011Reinhart, K. O. & Rinella, M. 2011. Comparing susceptibility of eastern and western US grasslands to competition and allelopathy from spotted knapweed (Centaurea stoebe L. subsp micranthos (Gugler) Hayek). Plant Ecology 212: 821–828. ).

Traditional, morphology-based treatments and their limitations

Section Centaurea is traditionally divided into two main groups based on the morphology of their bract appendages: section Phalolepis (Cass.) DC. (Fig. 1J) with lacerate membranaceous appendages, and sect. Centaurea (formerly sect. Acrolophus (Cass.) DC.; Fig. 1I) with ciliate to fimbriate ones. These two groups are treated as subgenera in Dostál (1976) in his treatment for Flora Europaea and more often as sections. The appendage morphology is the only character used for their delimitation (Dostál, 1976Dostál, J. 1976. Centaurea L. In: Tutin, T. G., Heywood, V. H., Burges, N. A., Moore, D. M., Valentine, D. H., Walters, S. M. & Webb, D. A. (Eds.), Flora Europaea 4. Plantaginaceae to Compositae (and Rubiaceae). Cambridge University Press, Cambridge, London, New York & Melbourne: 254–301. ), but within these two groups, however, a broad range of morphological characters can be found to perform further delimitations (Fig. 1L–N): leaf shape (divided), indumentum (tomentose, glabrous), flower colors (rarely yellow, mostly purple), plant size (a few centimetres in annual and biennial species up to 1.50 m in both biennial and perennial species, but mostly between 20 and 50 cm). A third section was upgraded to sectional rank 30 years ago: under the name of sect. Willkommia Blanca (Blanca, 1981aBlanca, G. 1981a. Revisión del género Centaurea L. sect. Willkommia G. Blanca nom. nov. Lagascalia 10: 131–205. ; Fig. 1K) a group of species was defined which shows perennial life form (frequently dwarf shrubs) and usually black, fimbriate bract appendages ending in a small spine. This group, contrarily to the other two sections, was defined also geographically as including only individuals from NW Africa and the Iberian Peninsula, but leaving behind morphologically similar forms from the Eastern Mediterranean. The delimitation between these three sections is more than problematic. The distinction between sections Phalolepis and Centaurea is based on one single morphological character and is thereafter highly questionable if this single character shows intermediate forms or is not present at all (as in some species from the central Mediterranean, where the bract appendages are totally or almost totally reduced). The presence of intermediate forms was demonstrated by Wagenitz (1989Wagenitz, G. 1989. Nahe Verwandtschaft zwischen Arten der Centaurea-Sektionen Acrolophus und Phalolepis. Flora 182: 341–351. ) and appears in many species descriptions (e.g. Breitwieser & Podlech, 1986Breitwieser, I. & Podlech, D. 1986. Die Gattung Centaurea L. sect. Willkommia G. Blanca in Nord-Afrika. Mitteilungen der Botanischen Staatsammlung München 22: 21–96. ; López & Devesa, 2008cLópez, E. & Devesa, J. A. 2008c. Notas taxonómicas sobre el género Centaurea L. (Asteraceae) en la Península Ibérica. I. C. cordubensis Font Quer, C. bethurica E. López & Devesa, sp. nov., y C. schousboei Lange. Anales del Jardin Botánico de Madrid 65: 331–341. ). Intermediate forms have been commonly attributed to hybridization between the two sections, without doubting their monophyly (Garcia-Jacas et al., 2006Garcia-Jacas, N., Uysal, T., Romaschenko, K., Suárez-Santiago, V. N., Ertuğrul, K. & Susanna, A. 2006. Centaurea revisited: A molecular survey of the Jacea group. Annals of Botany 98: 741–753. ; Suárez-Santiago et al., 2007bSuárez-Santiago, V. N., Salinas, M. J., Garcia-Jacas, N., Soltis, P. S., Soltis, D. E. & Blanca, G. 2007b. Reticulate evolution in the Acrolophus subgroup (Centaurea L., Compositae) from the western Mediterranean: Origin and diversification of section Willkommia Blanca. Molecular Phylogenetics and Evolution 43: 156–172. ).

Delimitation and monophyly of section Willkommia is not clear. In the Eastern Mediterranean, C. attica Nyman from Greece shows similar bract appendages, and similar species are also found in NE Libya (C. cyrenaica Bég. & A. Vacc.) and on the easternmost shore of the Mediterranean, for example C. damascena Boiss. and C. dumulosa. Boiss. All these species are currently assigned to sect. Centaurea. Intermediates between sections Willkommia and Centaurea are frequent on the Iberian Peninsula, where most members of section Centaurea show somewhat fimbriate and at least slightly spiny bract appendages. Placement of species like C. cordubensis and C. monticola in any of these two sections is unclear, which can also be seen in incongruencies between taxonomic treatments (Blanca, 1981aBlanca, G. 1981a. Revisión del género Centaurea L. sect. Willkommia G. Blanca nom. nov. Lagascalia 10: 131–205. vs. López & Devesa, 2008cLópez, E. & Devesa, J. A. 2008c. Notas taxonómicas sobre el género Centaurea L. (Asteraceae) en la Península Ibérica. I. C. cordubensis Font Quer, C. bethurica E. López & Devesa, sp. nov., y C. schousboei Lange. Anales del Jardin Botánico de Madrid 65: 331–341. ). Delimitation between Willkommia and Phalolepis following sole morphological observations is not precise either. Partly or entirely membranaceous bract appendages within Willkommia are found in NW Africa (C. debdouensis Breitw. & Podlech, C. pomeliana Batt.) and in the Iberian Peninsula (C. avilae Pau). Centaurea tougourensis Boiss. & Reut., one of the only two Phalolepis species from NW Africa, has a perennial, subshrubby life form and a small spine on their otherwise membranaceous bract appendages—very similar to members of section Willkommia, of which it is surrounded by.

Besides the separation of these three subgenera, Dostál (1975Dostál, J. 1975. New nomenclatural combinations and taxa of the Compositae subtribe Centaureinae in Europe. In: Heywood, V. H. (Ed.), Flora Europaea. Notulae Systematicae ad Floram Europaeam spectantes. Botanical Journal of the Linnean Society 71: 191–210. , 1976Dostál, J. 1976. Centaurea L. In: Tutin, T. G., Heywood, V. H., Burges, N. A., Moore, D. M., Valentine, D. H., Walters, S. M. & Webb, D. A. (Eds.), Flora Europaea 4. Plantaginaceae to Compositae (and Rubiaceae). Cambridge University Press, Cambridge, London, New York & Melbourne: 254–301. ) distinguished two subgroups within his subgenus Phalolepis and 11 within Acrolophus, stressing for their delimitation upon morphology of leaves, indumentum and bract appendages. Further groupings within the three sections are used in local treatments, for example in Pignatti (1982Pignatti, S. 1982. Flora d’Italia, 3. Edagricole, Bologna. ).

Hybridisation

The morphologically described species of sect. Centaurea are not separated through intrinsic breeding barriers. Reports about hybrids are abundant (e.g. Halácsy, 1902Halácsy, E. 1902. Conspectus Florae Graecae 2. Wilhelm Engelmann, Leipzig. ; Georgiadis, 1981aGeorgiadis, T. 1981a. Problèmes de différenciation et d’introgression dans Centaurea subg. Acrolophus (Compositae) en Grèce. Botanische Jahrbücher für Systematik, Pflanzengeschichte und Pflanzengeographie 102: 321–337. ; Blanca, 1984Blanca, G. 1984. Sobre algunas centaureas del sur de España. Lazaroa 6: 169–174. ). These hybrids are frequently fertile and homoploid (Blanca, 1981aBlanca, G. 1981a. Revisión del género Centaurea L. sect. Willkommia G. Blanca nom. nov. Lagascalia 10: 131–205. ; Ochsmann, 1998Ochsmann, J. 1998. Ein Bestand von Centaurea × psammogena Gáyer (Centaurea diffusa Lam. × Centaurea stoebe L.) am NSG Sonnenstein (Thüringen). Floristische Rundbriefe 31: 118–125. ; Pisanu et al., 2011Pisanu, S., Mameli, G., Farris, E., Binelli, G. & Filigheddu, R. 2011. A natural homoploid hybrid between Centaurea horrida and Centaurea filiformis (Asteraceae) as revealed by morphological and genetic traits. Folia Geobotanica 46: 69–86. ), sometimes also polyploid (Blair & Hufbauer, 2010Blair, A. C. & Hufbauer, R. A. 2010. Hybridization and invasion: one of North America’s most devastating invasive plants shows evidence for a history of interspecific hybridization. Evolutionary Applications 3: 40–51. ; Mráz et al., 2012Mráz, P., Garcia-Jacas, N., Gex-Fabry, E., Susanna, A., Barres, L. & Müller-Schärer, H. 2012. Allopolyploid origin of highly invasive Centaurea stoebe s. l. (Asteraceae). Molecular Phylogenetics and Evolution 62: 612–623. ). Hybrids with not closely related species—for example from the WMC—have been reported (Pau, 1914Pau, C. 1914. Sobre algunos vegetales curiosos. Boletín de la Sociedad Aragonesa de Ciencias Naturales 13: 42–44. ; Prodan, 1930Prodan, J. 1930. Centaureele Romăniei (Centaureae Romaniae): monographie. Institutul de Arte Grafice Ardealul, Cluj [in Romanian]. ; A. Susanna, pers. obs.), these however, produce usually no fertile offspring and therefore they do not lead to reticulation.

Systematic treatments of sect. Centaurea in light of molecular approaches

From the late 1990s onwards, a series of molecular investigations in sect. Centaurea has been conducted, using mainly DNA sequence data (Ochsmann, 2000Ochsmann, J. 2000. Morphologische und molekularsystematische Untersuchungen an der Centaurea stoebe L. Gruppe (Asteraceae – Cardueae) in Europa. Dissertationes Botanicae 324: 1–133. ; Garcia-Jacas et al., 2006Garcia-Jacas, N., Uysal, T., Romaschenko, K., Suárez-Santiago, V. N., Ertuğrul, K. & Susanna, A. 2006. Centaurea revisited: A molecular survey of the Jacea group. Annals of Botany 98: 741–753. ; Wagenitz et al., 2006Wagenitz, G., Hellwig, F. H., Parolly, G. & Martins, L. 2006. Two new species of Centaurea (Compositae, Cardueae) from Turkey. Willdenowia 36: 423–435. ; Suárez-Santiago et al., 2007bSuárez-Santiago, V. N., Salinas, M. J., Garcia-Jacas, N., Soltis, P. S., Soltis, D. E. & Blanca, G. 2007b. Reticulate evolution in the Acrolophus subgroup (Centaurea L., Compositae) from the western Mediterranean: Origin and diversification of section Willkommia Blanca. Molecular Phylogenetics and Evolution 43: 156–172. ; Beltrame, 2007Beltrame, C. 2007. Problèmes posés par le concept d’espèce en biologie de la conservation – exemple des centaurées de la section Maculosae dans les régions méditerranéenne et alpine de l’Europe occidentale. PhD Thesis, Université Pierre & Marie Curie, Paris. ; Mráz et al., 2012). Additionally, some work has been done, considering small species groups and using microsatellites techniques (Marrs et al., 2006Marrs, R. A., Hufbauer, R. A., Bogdanowicz, S. M. & Sforza, R. 2006. Nine polymorphic microsatellite markers in Centaurea stoebe L. [subspecies C. s. stoebe and C. s. micranthos (S. G. Gmelin ex Gugler) Hayek] and C. diffusa Lam. (Asteraceae). Molecular Ecology Notes 6: 897–899. ; Suárez-Santiago et al., 2007aSuárez-Santiago, V. N., Blanca, G., Ruiz-Rejón, M. & Garrido-Ramos, M. A. 2007a. Satellite-DNA evolutionary patterns under a complex evolutionary scenario: the case of Acrolophus subgroup (Centaurea L., Compositae) from the western Mediterranean. Gene 404: 80–92. ), isozymes (Bancheva et al., 2006Bancheva, S., Geraci, A. & Raimondo, F. M. 2006. Genetic diversity in the Centaurea cineraria (Compositae) in Sicily using isozymes. Plant Biosystems 140: 10–16. , 2011Bancheva, S., Geraci, A. & Raimondo, F. M. 2011. Assessing the genetic diversity of Centaurea parlatoris group (sect. Dissectae, Compositae) in Sicily using isozymes. Plant Biosystems 145: 778–785.), RAPD (Tornadore et al., 2000Tornadore, N., Marchiori, S. & Vergari, G. 2000. Systematic relationship of three species of Centaurea L. (Asteraceae) in Salento-Apulia (SE Italy). Israel Journal of Plant Sciences 48: 53–57. ; Sozen & Ozaydin, 2010Sozen, E. & Özaydyn, B. 2010. A study of genetic variation in endemic plant Centaurea wiedemanniana by using RAPD markers. Ekoloji 19: 1–8. ) and SDS-PAGE (Uysal et al., 2010). Interestingly, the traditional sectional division based on morphological traits was not confirmed in any of these molecular works.

Species delimitation within sect. Centaurea

As taxonomic treatments within sect. Centaurea are highly incongruent, a really crucial question arises: what has to be considered as a species and what not? From the answer of this question depend many other investigations, like the diagnosis of the conservation status and conservation strategies (e.g. Townsend-Peterson & Navarro-Sigüenza, 1999Townsend-Peterson, A. & Navarro-Sigüenza, A. G. 1999. Alternate species concepts as bases for determining priority conservation areas. Conservation Biology 13: 427–431. ). Modern species concepts agree in the point that species are separately evolving metapopulation lineages (De Queiroz, 2007De Queiroz, K. 2007. Species concepts and species delimitation. Systematic Biology 56: 879–886. ), but members of the genus Centaurea, like most other plant species as well, were and are still described following a purely phenetic species concept (Michener, 1970Michener, C. D. 1970. Diverse approaches to systematics. Evolutionary Biology 4: 1–38. ), i.e. only by assessing morphological characters in the hope that all populations bearing these characters would correspond to a single lineage. This approach itself may be prone to produce inaccurate results, but even more difficult is the question how much morphological divergence is enough to separate two morphologically distinct plant groups as separate species. Additionally, the same or similar characters may arise separately and may therefore not be synapomorphies but rather homoplasic traits. Differences in species numbers produced by different modi operandi are huge. Examples can be easily seen if we compare different taxonomic treatments in Centaurea.

Species List

The following list includes all species of the newly defined section Centaurea (including former sections Acrolophus, Phalolepis and Willkommia). Only recent literature is incorporated. Taxonomy follows Euro+Med Plantbase (Euro+Med, 2006–2013Euro+Med. 2006–2013. Euro+Med Plantabase – The information resource for Euro-Mediterranean plan diversity. Compositae. Retrieved November, 2013, from http://ww2.bgbm.org/EuroPlusMed/.), which is the most complete listing of the genus Centaurea. For areas not included in Euro+Med, local floras were used. Cases where our treatment diverges from that of Euro+Med are specifically mentioned. Synonyms are only given if the name in Euro+Med diverges from the name used in this list. The second column of the Table 2 shows the currently accepted assignation to any of the three subsections Centaurea (C, formerly sect. Acrolophus), Phalolepis (P) and Willkommia (W). The third column shows the approximate distribution of the taxon. The fourth column gives information about the chromosome number. We usually give two citations per chromosome number, because further information can be easily retrieved from the indices to plant chromosome numbers (Goldblatt & Johnson, 1979Goldblatt, P. & Johnson, D. E. (Eds.) 1979–. Index to plant chromosome numbers. Missouri Botanical Garden, St. Louis. Retrieved May 24, 2012, from http://www.tropicos.org/Project/IPCN. –; Watanabe, 2002Watanabe, K. 2002. Index to chromosome numbers in Asteraceae. Retrieved February, 2014, from http://www.lib.kobe-u.ac. jp/infolib/meta_pub/G0000003asteraceae_e). The fifth column shows if there exists evidence from the ITS that the taxon belongs to the section Centaurea. The information derives, if not otherwise mentioned, from the studies of Ochsmann (2000Ochsmann, J. 2000. Morphologische und molekularsystematische Untersuchungen an der Centaurea stoebe L. Gruppe (Asteraceae – Cardueae) in Europa. Dissertationes Botanicae 324: 1–133. ), Garcia-Jacas et al. (2006Garcia-Jacas, N., Uysal, T., Romaschenko, K., Suárez-Santiago, V. N., Ertuğrul, K. & Susanna, A. 2006. Centaurea revisited: A molecular survey of the Jacea group. Annals of Botany 98: 741–753. ), Suárez-Santiago et al. (2007aSuárez-Santiago, V. N., Blanca, G., Ruiz-Rejón, M. & Garrido-Ramos, M. A. 2007a. Satellite-DNA evolutionary patterns under a complex evolutionary scenario: the case of Acrolophus subgroup (Centaurea L., Compositae) from the western Mediterranean. Gene 404: 80–92. , 2007bSuárez-Santiago, V. N., Salinas, M. J., Garcia-Jacas, N., Soltis, P. S., Soltis, D. E. & Blanca, G. 2007b. Reticulate evolution in the Acrolophus subgroup (Centaurea L., Compositae) from the western Mediterranean: Origin and diversification of section Willkommia Blanca. Molecular Phylogenetics and Evolution 43: 156–172. ) and Hilpold et al. (2014Hilpold, A., Vilatersana, R., Susanna, A. et al. 2014. Phylogeny of the Centaurea group (Centaurea, Compositae) – geography is a better predictor than morphology. Molecular Phylogenetics and Evolution 77: 195–215.). Column six lists revisions of the species when available. The last column gives information about the existence of subspecies (only those accepted in Euro+Med).

Iberian Peninsula —Systematic treatment follow the preparatory works for Flora iberica by López & Devesa (2008aLópez, E. & Devesa, J. A. 2008a. Notas taxonómicas sobre el género Centaurea L. (Asteraceae) en la Península Ibérica. II. C. castellanoides Talavera y C. aristata Hoffmanns. & Link. Acta Botanica Malacitana 33: 57–68. , 2008bLópez, E. & Devesa, J. A. 2008b. Notas taxonómicas sobre el género Centaurea L. (Asteraceae) en la Península Iberica. III. Centaurea limbata Hoffmanns. & Link. Lagascalia 28: 411–423. , 2088cLópez, E. & Devesa, J. A. 2008c. Notas taxonómicas sobre el género Centaurea L. (Asteraceae) en la Península Ibérica. I. C. cordubensis Font Quer, C. bethurica E. López & Devesa, sp. nov., y C. schousboei Lange. Anales del Jardin Botánico de Madrid 65: 331–341. , 2010López, E. & Devesa, J. A. 2010. Notas taxonómicas sobre el género Centaurea (Asteraceae) en la Península Ibérica. C. paniculata, C. hanryi y C. diffusa. Anales del Jardin Botánico de Madrid 67: 113–126. , 2011López, E. & Devesa, J. A. 2011. Revisión taxonómica del complejo Centaurea alba L. (Asteraceae) en la Península Ibérica. Collectanea Botanica (Barcelona) 30: 37–52. ) and López et al. (2011López, E., Devesa, J. A. & Arnelas, I. 2011. Taxonomic study in the Centaurea langei complex. Annales Botanici Fennici 48: 1–12. ) for the C. paniculata and the C. alba groups, and Blanca & Suárez-Santiago (2011Blanca, G. & Suárez-Santiago, V. N. 2011. Centaurea boissieri DC. y C. resupinata Coss. (Asteraceae) en la Península Ibérica. Acta Botanica Malacitana 36: 89–105. ) for sect. Willkommia. Identification keys can be found in López & Devesa (2010López, E. & Devesa, J. A. 2010. Notas taxonómicas sobre el género Centaurea (Asteraceae) en la Península Ibérica. C. paniculata, C. hanryi y C. diffusa. Anales del Jardin Botánico de Madrid 67: 113–126. ; C. paniculata complex & C. diffusa), López & Devesa (2011López, E. & Devesa, J. A. 2011. Revisión taxonómica del complejo Centaurea alba L. (Asteraceae) en la Península Ibérica. Collectanea Botanica (Barcelona) 30: 37–52. ; C. alba complex) and Blanca (1981aBlanca, G. 1981a. Revisión del género Centaurea L. sect. Willkommia G. Blanca nom. nov. Lagascalia 10: 131–205. ) for members of sect. Willkommia. Whether C. paniculata and C. leucophaea Jord. from the Iberian Peninsula are really closely related or even homonymous to populations from SE France and NE Italy is an open question. The same is true for Centaurea boissieri DC., C. monticola Boiss. ex DC. and C. resupinata Coss., all listed for the Iberian Peninsula and NW Africa.

North Africa — Most members of sect. Centaurea occur in the NW of the continent, namely in various ranges of the Atlas Mountains. Only C. cyrenaica Bég. & A. Vacc. occurs in the NE of the continent (Lybia). No recent complete treatments of the group are available, only the revision of section Willkommia from NW Africa by Breitwieser & Podlech (1986).

Italy, France and central Europe — All Italian Centaurea species are listed in Conti et al. (2005D’Amato, G. & Pavesi, A. 1990. Numeri cromosomici per la flora italiana: 1247–1250. Informatore Botanico Italiano 22: 244–246. ) and in Network Nazionale della Biodiversità (2012–Network Nazionale della Biodiversità. 2012–. Checklist della flora vascolare d’Italia. Retrieved February 15, 2012, from http://dbiodbs1.units. it/checklist/index.php) but are not treated in detail. Complete treatments for Italy are given in Fiori (1927Fiori, A. 1927. Nuova flora analitica d’Italia 2. M. Ricci, Firenze. ) and in Pignatti (1982Pignatti, S. 1982. Flora d’Italia, 3. Edagricole, Bologna. ). Treatments for single groups: Arrigoni (2003Arrigoni, P. V. 2003. Le Centauree italiane del gruppo “Centaurea paniculata L.”. Parlatorea 6: 49–78. ; C. paniculata complex), Cela Renzoni & Viegi (1982Cela Renzoni, G. & Viegi, L. 1982. Centaurea cineraria s. l. (Asteraceae) in Italia: Revisione citotassonomica. Atti della Società Toscana di Scienze Naturali di Pisa, Memorie, Serie B 39: 99–144. ; C. cineraria complex); Guarino & Rampone (2006Guarino, C. & Rampone, S. 2006. A morphometric analysis of Centaurea sect. Dissectae (Compositae). Bocconea 19: 77–88. ; C. dissectae group). Many new descriptions have been published over the last 30 years. In the meantime, C. subtilis has been removed form the section (Hilpold et al., 2009Hilpold, A., Garcia-Jacas, N., Vilatersana, R. & Susanna, A. 2009. Two additions to the Jacea-Lepteranthus complex: Parallel adaptation in the enigmatic species Centaurea subtilis and C. exarata. Collectanea Botanica (Barcelona) 28: 47–58. ). Here we follow the very tight treatment of Euro+Med.

Balkans (including Romania, Aegean Sea and Crete) — The most complete taxonomic treatments concentrating on the Balkan area are those of Boissier (1875Boissier, E. 1875. Flora Orientalis sive enumeratio plantarum in Oriente a Graecia et Aegypto ad Indiae fines hucusque observatarum 3. H. Georg, Geneva & Basel. ) and Hayek (1931Hayek, A. von. 1931. Prodromus Florae Peninsulae Balcanicae 2. Feddes Repertorium Supplements 30. ). Newer treatments of the entire area other than Flora Europaea (Dostál, 1976Dostál, J. 1976. Centaurea L. In: Tutin, T. G., Heywood, V. H., Burges, N. A., Moore, D. M., Valentine, D. H., Walters, S. M. & Webb, D. A. (Eds.), Flora Europaea 4. Plantaginaceae to Compositae (and Rubiaceae). Cambridge University Press, Cambridge, London, New York & Melbourne: 254–301. ) do not exist. In the NW Balkans, besides some widely distributed species, there are two main species groups: the C. spinosociliata group and the C. cuspidata group. The latter one, though only distributed in a relatively small area, was split into several microspecies of doubtful rank. These two species groups are treated in Lovrić (1968Lovrić, A. Ž. 1968. Prilog poznavanju ilirskih Centaureja s posebnim obzirom na sekciju Pterolophus (Cass.) DC. [Contribution to the study of Illyrian Centaurea, with special attetion to section Pterolophus (Cass.) DC.]. Acta Botanica Croatica 27: 263–278 [in Croatian]. ). A treatment for Romania is given in Ciocârlan (2000Ciocârlan, V. 2000. Flora ilustrată a României [Illustrated flora of Romania]. Ed. Ceres, Bucharest [in Romanian]. ), for Greece in Halácsy, (1902Halácsy, E. 1902. Conspectus Florae Graecae 2. Wilhelm Engelmann, Leipzig. ), for the Greek Mountains in Gamal-Eldin & Wagenitz (1991Gamal-Eldin, E. & Wagenitz, G. 1991. Centaurea L. In: Strid, A. & Tan, K. (Eds.), Mountain flora of Greece 2. Edinburgh University Press, Edinburgh: 488–524. ), for the Aegean Sea in Rechinger (1943Rechinger, K. H. 1943. Flora Aegaea. Flora der Inseln und Halbinseln des Ägäischen Meeres. Österreichische Akademie der Wissenschaften, Mathematisch-Naturwissenschaftliche Klasse, Denkschriften 105. ), for N Greece in Rechinger (1939Rechinger, K. H. 1939. Zur Flora von Ostmazedonien und Westthrazien. Botanische Jahrbücher für Systematik, Pflanzengeschichte und Pflanzengeographie 69: 419–552. ). Listings of sect. Phalolepis from Greece are given in Wagenitz (1971Wagenitz, G. 1971. Centaurea pseudocadmea, eine neue Art der Sektion Phalolepis aus Griechenland. Annalen des Naturhistorischen Museums in Wien 75: 243–247. ) and Georgiadis et al. (1996Georgiadis, T., Dimitrellos, G. & Routsi, E. 1996. Centaurea messenicolasiana (Asteraceae), a new species of C. sect. Phalolepis (Cass.) DC. from Greece. Willdenowia 25: 561–569. ), of the Bulgarian members of genus Centaurea in Assyov et al. (2002Assyov, B., Dimitrov, D., Vassilev, R. & Petrova, A. 2002. Conspectus of the Bulgarian vascular flora. Bulgarian-Swiss Biodiversity Conservation Programme, Sofia. ) of the Croatian members in Flora Croatica Database (Nikolić, 2010Nikolić, T. 2010. Flora Croatica Database. University of Zagreb, Zagreb. Retrieved February 15, 2012, from http://hirc.botanic.hr/fcd. ).

Region N of Black Sea (Russia p. p., Ukraine, Moldavia) — Most species in this area belong to five species groups: the C. stoebe complex, the C. margaritacea aggr., the C. sterilis aggr., the C. ovina aggr. and the C. arenaria aggr. Monophyly of these groups is not clear. The most complete treatment for Russia, Ukraine and Moldavia is given in Klokov et al. (1963Klokov, M. B., Sosnovskii, D. I., Tzvelev, N. N. & Czerepanov, C. K. 1963. Centaurea. In: Bobrov, E. G. & Czerepanov, S. K. (Eds.), Flora USSR 28. Institutum Botanicum nomine V. Komarovii Academia Scientiarum USSR. Editio Academia Scientiarum Moskow, Moscow & Saint Petersburg: 370–579. ).

Anatolia and Cyprus — Flora of Turkey (Wagenitz, 1975Wagenitz, G. 1975. Centaurea L. In: Davis, P. H. (Ed.), Flora of Turkey and the East Aegean Islands 5. Edinburgh University Press, Edinburgh: 465–485. ) lists nine species for section Phalolepis and 21 species for section Centaurea (= Acrolophus). In recent years, several new species have been described. Two species of Phalolepis (C. hierapolitana and C. tossiensis) do not belong to sect. Centaurea. The same is true for C. akamantis from Cyprus—where only one species remains, C. cyprensis (Holub) T. Georgiadis (Meikle, 1985Meikle, R. D. 1985. Flora of Cyprus 2. The Bentham-Moxton Trust – Royal Botanic Gardens, Kew. ).

Caucasus Region — The Caucasus region, including parts of Russia, Georgia, Armenia and Azerbaijan, is relatively poor in endemic taxa of sect. Centaurea. The most complete treatment for the area is given in Klokov et al. (1963Klokov, M. B., Sosnovskii, D. I., Tzvelev, N. N. & Czerepanov, C. K. 1963. Centaurea. In: Bobrov, E. G. & Czerepanov, S. K. (Eds.), Flora USSR 28. Institutum Botanicum nomine V. Komarovii Academia Scientiarum USSR. Editio Academia Scientiarum Moskow, Moscow & Saint Petersburg: 370–579. ).

Near-East, Middle-East — No complete listings or treatments are available postdating Boissier (1875Boissier, E. 1875. Flora Orientalis sive enumeratio plantarum in Oriente a Graecia et Aegypto ad Indiae fines hucusque observatarum 3. H. Georg, Geneva & Basel. ), since Euro+Med considers only the western part of this area. Contributions for this area in the list derive mainly from regional floras; i.e. Post & Dinsmore (1932Post, G. & Dinsmore, E. 1932. Flora of Syria, Palestine and Sinai 2. American University of Beirut, Beirut. ), Feinbrun-Dothan (1978Feinbrun-Dothan, N. 1978. Flora Palaestina 3, Ericaceae to Compositae. Israel Academy of Sciences and Humanities, Jerusalem. ) and Wagenitz (1980Wagenitz, G. 1980. Centaurea. In: Rechinger, K. H. (Ed.), Flora Iranica 139b. Akademische Druck-u. Verlagsanstalt, Graz: 313–420. ).

Nomenclatural proposals

Centaurea subgenus Lopholoma (Cass.) Dobrocz.

Sect. Acrocentron (Cass.) DC. subsect. Chamaecyanus (Willk.) Garcia-Jacas, Hilpold, Susanna & Vilatersana, new combination ≡ Centaurea sect. Chamaecyanus Willk. in Willkomm & Lange, Prodr. Fl. Hisp. 2: 150. 1870 [Basionym].

Centaurea subgenus Centaurea

Sect. Centaurea

Centaurea sect. Centaurea subsect. Phalolepis (Cass.) Garcia-Jacas, Hilpold, Susanna & Vilatersana, new combination ≡ Phalolepis Cass., Dict. Sci. Nat., ed. 2., 50: 248. 1827 [Basionym] ≡ Centaurea sect. Phalolepis (Cass.) DC., Prodr. 6: 568. 1838. ≡ Centaurea subgenus Phalolepis (Cass.) Dobrocz., Bot. Zurn. 6: 63. 1949. Fig. 1K.

Centaurea sect. Centaurea subsect. Willkommia (Blanca) Garcia-Jacas, Hilpold, Susanna & Vilatersana, new combination ≡ Centaurea sect. Willkommia Blanca, Lagascalia 10: 138. 1981 (publ. 1982) [Basionym]. Fig. 1L.

Centaurea sect. Akamantis Garcia-Jacas, Hilpold, Susanna & Vilatersana, new section

Perennial species with heterogamous heads. Cauline leaves linear-spatulathe, sparsely lanuginose. Capitula very small, exactly ovate. Bracts lanuginose; appendages much reduced, triangular, scariose, terminated in a short recurved mucro. All the florets deep purple, the central ones with darker anther-tube, the outer ones sterile, only slightly radiant.

Type and only species: Centaurea akamantis T. Georgiadis & Hadjik., Willdenowia 23: 157. 1993. Fig. 1E.

Centaurea sect. Cnicus (L.) Garcia-Jacas, Hilpold, Susanna & Vilatersana, new status and combination ≡ Cnicus L., Sp. Pl. 2: 826. 1753 (nom. cons.) [Basionym]. Type and only species: Centaurea benedicta L., Sp. Pl. 2: 826. 1753. Fig. 1D.

Centaurea sect. Hierapolitanae Garcia-Jacas, Hilpold, Susanna & Vilatersana, new section

Annual or perennial species with heterogamous heads. Capitula minute, cylindrical, with only 10-20 florets, the outer ones sterile and radiant. Involucral bracts with orbicular, scariose, lacerate appendages, similar to those of sect. Phalolepis, but long decurrent. Type: Centaurea hierapolitana Boiss., Diagn. Pl. Orient. ser. 1, 4: 15. 1844. Other species: Centaurea tossiensis Freyn & Sint., Oest. Bot. Zeitschr. 44: 258. 1894. Fig. 1F.

Centaurea sect. Phrygia

Centaurea sect. Phrygia subsect. Exarata, new subsection

Stands apart from subsect. Phrygia and subsect. Jacea by the reduced appendages of the bracts, which are very small, applicate, not plumose and recurved as in subsect. Phrygia or very wide and covering partly or totally the bracts as in subsect. Jacea. Differs from subsect. Subtilis by having entire leaves, not pinnatisect as in C. subtilis. Type and only species: Centaurea exarata Boiss. ex Coss., Notes pl. crit.: 116. 1851. Fig.1H.

Centaurea sect. Phrygia subsect. Jacea (L.) Garcia-Jacas, Hilpold, Susanna & Vilatersana, new combination ≡ Centaurea [infrageneric unranked] jacea L., Sp. Pl. 2: 909. 1753 [Basionym] ≡ Centaurea sect. Jacea (L.) DC., Prodr. 6: 570. 1837 [publ. 1838].

Centaurea sect. Phrygia subsect. Subtilis, new subsection

Can be easily set apart from subsect. Phrygia, subsect. Exarata and subsect. Jacea by the pinnatisect basal and mid-cauline leaves, which are entire in all the other subsections. Differs from sects. Jacea and Phrygia by the small and triangular bract appendages not covering the bracts. Type and only species: Centaurea subtilis Bertol., Flora Italica 9: 451. 1854.

ACKNOWLEDGEMENTSTop

Financial support from the Spanish Ministry of Science and Innovation (Projects CGL2007-60781/BOS and CGL2010-18631/BOS) and the Generalitat de Catalunya (Ajuts a Grups de Recerca Consolidats 2009/SGR/00439) is gratefully acknowledged. A. H. benefited from a predoctoral grant of the JAE program of the CSIC.

REFERENCESTop