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., 1995; Garcia-Jacas et al., 2000, 2001, 2006; Hilpold et al., 2014). To put it shortly, Centaurea as defined traditionally (e.g. Linnaeus, 1753; Bentham, 1873; Hoffmann, 1894; Dostál, 1976) 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., 2001). The old section Centaurea acquired the rank of genus on its own, namely Rhaponticoides Vaill. (Greuter, 2003; Greuter et al., 2005). 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, 2007). They are also characterized by a lateral hilum (Dittrich, 1968), and a specialized floral morphology with showy sterile peripheral florets without staminodes (Wagenitz & Hellwig, 1996a ). 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, 1995; Bilisik et al., 2008; Albrecht et al., 2009; McIver et al., 2009). 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, 2007, 2009), 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., 2008).

We published a general outline of a classification of the genus in Susanna & Garcia-Jacas (2007, 2009), 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.

For subgenera Cyanus and Lopholoma, our outline is based on the studies by Boršić et al. (2011) and Font et al. (2002, 2009), respectively. Regarding subg. Centaurea, our proposal follows the layout suggested by Garcia-Jacas et al. (2006) and Hilpold (2012), 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, 2006–2013) for the Eastern and Central Mediterranean region, and López & Devesa (2008a , 2008b , 2008c , 2008d , 2010c , 2011c ) and López et al., (2011c ) for the Iberian Peninsula. More details on the construction of the Table 2 are given below.

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., 2006). Cyanus has been also treated as separate genus (e.g. Greuter, 2003). 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., 2001; Susanna et al., 2006; Barres et al., 2013) and correspond to the existing pollen types.

The pollen of the genus Centaurea is, like that of all Compositae (Blackmore et al., 2009), tricolporate and the ectexine is formed by two layers of columellae (Wagenitz, 1955). Within the genus, four clearly distinct pollen types can be found, which correspond to the three subgenera (Wagenitz, 1955; Martín & Garcia-Jacas, 2000; Susanna & Garcia-Jacas, 2009). Centaureinae show a dysploid chromosome series, with basic chromosome numbers ranging between x = 16 and x = 7 (Garcia-Jacas et al., 1996). Low numbers can be found in more evolved groups and have been interpreted as an adaptation to dry conditions (Susanna & Garcia-Jacas, 2009). 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.

tabla 1

Centaurea is rich in secondary metabolites, which may mostly be a protection against herbivores (Olson & Kelsey, 1997; Susanna & Garcia-Jacas, 2009). Some of them show antimicrobial activity (Karioti et al., 2001; Ugur et al., 2009). Metabolites are predominantly sesquiterpene lactones (Tarasov et al., 1975; Koukoulitsa et al., 2005; Karamenderes et al., 2007), but also flavonoids (Zapesochnaya et al., 1978; Nacer et al., 2006), essential oils (Altintas et al., 2004) and phenols (Bubenchikov et al., 1992). 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., 2002) 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, 1955). This subgenus was studied applying molecular tools by Font et al. (2002, 2009). 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., 2002) and constitutes the first section. The second section, section Acrocentron, encompasses all other species of the subgenus. On molecular basis, Font et al. (2009) 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. (2011), Olšavská et al. (2011) and Löser (2013). The study of Boršić et al. (2011) 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).

Subgenus Centaurea

This subgenus corresponds to the Jacea group sensu Garcia-Jacas et al. (2006) 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, 1955; Garcia-Jacas et al., 2000). New systematic insights of the subgenus on molecular grounds were provided by Garcia-Jacas et al. (2006). 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. (2006) 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, 1996a ). Following Hilpold (2012), 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., 2011; López-Alvarado, 2012) 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., 2002; Koutecký et al., 2011; Vonica & Cantor, 2011). 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., 2000; Koutecký, 2007; Koutecký et al., 2011). 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; Koutecký, 2007; Vonica & Cantor, 2011). 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.).

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, 1995; Hardy et al., 2004). Reproduction is usually sexual (Noyes, 2007), although facultative apospory has been reported (Cela Renzoni & Viegi, 1982).

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., 2008; Mráz et al., 2012). Three species are hexaploid (2n = 6x = 54): C. carystea Trigas & Constantin., C. cithaeronea Phitos & Constantin. and C. tuzgoluensis Aytaç & H. Duman; cf. Phitos & Constantinidis, 1993; Martın et al., 2009; Trigas et al. 2008 , 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., 2006; Hilpold et al., 2009). 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, 1983; only in one out of many counts in C. diffusa Lam.; Bancheva & Greilhuber, 2006), and 2n = 32 (in C. arenaria Willd.; Bancheva & Greilhuber, 2006). Fig. 3 shows the percentages of counted species and the distribution of the known chromosome numbers.

A few members of sect. Centaurea are used as ornamentals, like Centaurea cineraria L. (“Velvet Centaurea”, cf. Ellis, 1999). Some species are used as medicinals, especially in folk medicine, because of its secondary compounds (Nacer et al., 2006; Akkol et al., 2009). 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., 1997; Erel et al., 2011) is sometimes used for bitter tonics (Tešević et al., 2007).

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, 2010), diminishes the fodder value of pastures infesting about 3 million ha (Di Tomaso, 2000) 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., 2001). The fight against these weeds is also the motor of most of the research conducted in Centaurea (e.g. Hufbauer & Sforza, 2008; Collins et al., 2011; Pollock et al., 2011; Reinhart & Rinella, 2011).

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, 1976), 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, 1981a ; 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 (1989) and appears in many species descriptions (e.g. Breitwieser & Podlech, 1986; López & Devesa, 2008c ). Intermediate forms have been commonly attributed to hybridization between the two sections, without doubting their monophyly (Garcia-Jacas et al., 2006; Suárez-Santiago et al., 2007b ).

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, 1981a vs. López & Devesa, 2008c ). 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 (1975, 1976) 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 (1982).

Hybridisation

The morphologically described species of sect. Centaurea are not separated through intrinsic breeding barriers. Reports about hybrids are abundant (e.g. Halácsy, 1902; Georgiadis, 1981a; Blanca, 1984). These hybrids are frequently fertile and homoploid (Blanca, 1981a ; Ochsmann, 1998a ; Pisanu et al., 2011), sometimes also polyploid (Blair & Hufbauer, 2010; Mráz et al., 2012). Hybrids with not closely related species—for example from the WMC—have been reported (Pau, 1914; Prodan, 1930; 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, 2000; Garcia-Jacas et al., 2006; Wagenitz et al., 2006; Suárez-Santiago et al., 2007b ; Beltrame, 2007; Mráz et al., 2012). Additionally, some work has been done, considering small species groups and using microsatellites techniques (Marrs et al., 2006; Suárez-Santiago et al., 2007a ), isozymes (Bancheva et al., 2006, 2011), RAPD (Tornadore et al., 2000; Sozen & Ozaydin, 2010) 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, 1999). Modern species concepts agree in the point that species are separately evolving metapopulation lineages (De Queiroz, 2007), 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, 1970), 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, 2006–2013), 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, 1979–; Watanabe, 2002). 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 (2000), Garcia-Jacas et al. (2006), Suárez-Santiago et al. (2007a, 2007b) and Hilpold et al. (2014). 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 (2008a, 2008b, 2008c, 2010, 2011) and López et al. (2011) for the C. paniculata and the C. alba groups, and Blanca & Suárez-Santiago (2011) for sect. Willkommia. Identification keys can be found in López & Devesa (2010; C. paniculata complex & C. diffusa), López & Devesa (2011; C. alba complex) and Blanca (1981a) 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. (2005) and in Network Nazionale della Biodiversità (2012) but are not treated in detail. Complete treatments for Italy are given in Fiori (1927) and in Pignatti (1982). Treatments for single groups: Arrigoni (2003; C. paniculata complex), Cela Renzoni & Viegi (1982; C. cineraria complex); Guarino & Rampone (2006; 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., 2009). 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 (1875) and Hayek (1931). Newer treatments of the entire area other than Flora Europaea (Dostál, 1976) 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 (1968). A treatment for Romania is given in Ciocârlan (2000), for Greece in Halácsy, (1902), for the Greek Mountains in Gamal-Eldin & Wagenitz (1991), for the Aegean Sea in Rechinger (1943), for N Greece in Rechinger (1939). Listings of sect. Phalolepis from Greece are given in Wagenitz (1971) and Georgiadis et al. (1996), of the Bulgarian members of genus Centaurea in Assyov et al. (2002) of the Croatian members in Flora Croatica Database (Nikolić, 2010).

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. (1963).

Anatolia and Cyprus — Flora of Turkey (Wagenitz, 1975) 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, 1985).

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. (1963).

Near-East, Middle-East — No complete listings or treatments are available postdating Boissier (1875), 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 (1932), Feinbrun-Dothan (1978) and Wagenitz (1980).

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.

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