Centaurea dolopica Zograf., Koutroumpa, Liveri & Dimop., 2023

Zografidis, Aris, Koutroumpa, Konstantina, Liveri, Eleni & Dimopoulos, Panayotis, 2023, Centaurea dolopica (Asteraceae, Cardueae), a new species of section Acrocentron from Greece, Phytotaxa 584 (3), pp. 173-185 : 176-183

Centaurea dolopica Zograf., Koutroumpa, Liveri & Dimop. , sp. nov.

Diagnosis:—A species belonging to the Centaurea achaia group (including C. achaia , C. aetolica , C. corinthiaca and C. euboica ) and distinguished from the other members by its narrower involucral bracts and by its fewer central florets. Robust individuals of C. dolopica also exhibit larger and more branched flowering stems bearing a larger number of capitula.

Type :— GREECE. Nomos Fthiotidos , Eparchia Domokou: ca. 10 km W of Omvriaki, scrub on serpentine cut slope and roadsides, 440 m, 39°06’N, 22°09’E, 15 July 2022, Zografidis 745 (holotype: UPA (39986 & 39987)! mounted on two sheets; isotypes: ATH!, B!) ( Figs 1 , 2 , 3 ( A, B), 4(e)) .

Robust, densely arachnoid, perennial herb with one to several leaf rosettes and one to several (40 counted in a large individual) erect flowering stems 40–100(–120) cm in length, often bent in maturity by the weight of their capitula. Flowering stems branched from below middle (in robust, much-branched stems) or above middle (in sparingly branched stems) with 1–11 branches, forming pseudopaniculate-subcorymbose synflorescences, each flowering stem bearing 3–29 capitula. Basal, late successional rosette leaves and lower cauline leaves 1- to 2-pinnatisect to pinnate, ovate-elliptical to oblong-lanceolate in outline, 10–55 × 3–15 cm with a petiole up to 18 cm; segments ca. 8–12, simple or 1-pinnatisect, attenuate, frequently subtended or intermitted by smaller, simple segments. Simple segments of basal leaves elliptical to narrowly oblong-lanceolate or oblanceolate, up to 10 × 1 cm, subacute-mucronate to acute; margins subentire to irregularly denticulate, rarely lobed. Middle and upper cauline leaves gradually reduced in size and lobe number, the uppermost simple. Capitula 3–3.8 × 2.5–3.4 cm; involucre ovoid to ellipsoid-ovoid, 1.8–2.6 × 0.9–1.5 cm; receptacle 5–9 mm in diameter, densely setose; setae 5–11 mm long, caducous in fruiting stage; involucral bracts in several rows, imbricate, coriaceous, with appendages ± covering the bracts; middle bracts 0.8–1.8 × 0.3–0.5 cm (incl. appendage); appendage of middle bracts slightly convex, spiny, fimbriate, decurrent, straw-colored to brownish, 0.47–1.32 × 0.57–1.35 cm, with (5-)8–14 cilia 0.16–0.51 cm in length on each side and a spine 0.1–0.8 cm. Florets purplish; marginal, sterile florets 10–18, 2.2–3.2 cm in length, radiant, with 3–5(–6) lobes ca. 1 cm in length; central florets 23–39, hermaphrodite, tubular, expanded into 5-lobed corolla, 2.3–3.4 cm in length; anthers syngenesious, oblong, ca. 4 mm in length. Achenes straw-colored to dark greyish with caducous hairs and a lateral hilum. Outer achenes oblong to narrowly oblong 3.2–4.9 × 0.9–1.6 mm; pappus of outer achenes consisting of one series of smooth hairs, 1.2–4 mm in length. Central (fertile) achenes ovoid-oblong, 4.1–5.3 × 1.9–2.8 mm, with a pappus of two rows, the inner row consisting of smooth hairs, the outer row consisting of scabrous hairs; larger hairs of inner row 2.5–4.5 mm; larger hairs of outer row 7.5–11.5 mm.

Etymology: —The specific epithet of the new species refers to Dolopia, the ancient name of the region where the plants were found.

Phenology: —The first capitula open in early July and anthesis peaks in mid-July followed by fruiting of the plants in late July and August.

Karyology: —The karyotype formula of Centaurea dolopica is 2 n = 8m +2m-SAT+2sm+2sm-SAT = 22 chromosomes. The karyotype of the new species is diploid (2 n = 2x = 22) and symmetrical. It consists of metacentric (m) and submetacentric (sm) chromosomes ( Fig. 5 ). The 3rd largest in size chromosome pair is submetacentric. The 8th and 9th chromosome pairs are submetacentric and metacentric, respectively, whereas both are bearing small spherical satellites. The size of the chromosomes varies between 1.51–3.49 μm and the average chromosome length (ACL) equals to 2.43 μm. THL and TCL equal to 26.77 μm and 53.54 μm, respectively.

Distribution and habitat: —Based on the current knowledge, Centaurea dolopica is restricted to a single, small population located along a provincial road ca. 10 km west of the settlement of Omvriaki in Nomos Fthiotidos, Central Greece. The substrate of the gently hilly landscape is ophiolitic and the vegetation is characterized by a Quercus coccifera Linnaeus (1753: 995) partly evergreen scrub (pseudomaquis). The Centaurea plants grow mainly on the roadsides and the rocky cut slope ( Fig. 3A,B ), whereas only a few plants were observed inside the surrounding denser scrub. We note that cut slopes—resembling natural steep slopes—and roadsides are frequently inhabited by this photophilous and often chasmophytic genus, and the plants may be more sporadic or even absent from the surrounding, undisturbed vegetation (e.g., Phitos et al. 2009, Zografidis et al. 2014). Interestingly, among the angiosperms observed and collected in the habitat of C. dolopica , was Eryngium serbicum Pančić (1856: 520) ( Fig. 3C ) (voucher Zografidis 743 UPA!), which represents the first confirmed report from Greece of this conspicuous and characteristic Balkan endemic species. Since the new Centaurea and the eryngo species could easily be observed by any botanist traversing this location west of Omvriaki during mid to late summer, the fact that these two species were only currently recorded indicate that the region must have long remained floristically unexplored. A collection by Hartvig et al. 10541 (C) from north of Trilofon, assigned to C. achaia by Wagenitz & Gamal-Eldin (1985), was of interest to be studied due to its geographical proximity to C. dolopica , namely just ca. 10 km south of the locus classicus. However, despite our exhaustive search in herbarium C, we could not trace this material and neither did we succeed in finding the respective population of plants in the field. The examination of a duplicate specimen of the aforementioned collection kept in a private herbarium indicated that the taxonomic identity of the specimen is unsettled due to the fact that it was collected late in the season, perhaps representing a regrowth after the plant had been cut or bitten down, and is in poor condition (Arne Strid, pers. comm.). A more detailed field exploration is needed to locate this population of Centaurea and to re-examine its taxonomic status.

Conservation assessment: —The sole known population of the new species is very small and restricted. The plants were found along ca. 300 m of the provincial road (see above), accounting for an area of occupancy of well below 1 km 2. Approximately 70 mature and 40 immature plants were counted. Centaurea dolopica was only recently observed for the first time and no estimation on the size of its population in the past can be drawn. However, given that Centaurea spp. of section Acrocentron are impressive herbs and sought for by professional and amateur botanists alike, it can be assumed that the new species has been a very rare plant throughout the last century at least. Quercus coccifera pseudomaquis in Greece has generally been considered secondary vegetation ( Chasapis et al. 2004 and references therein), but no indication of ongoing decline of the quality of habitat (including grazing) was observed or estimated. The widening of the provincial road would certainly be detrimental for the plants that grow along roadsides, but road upgrading construction works are considered unlikely at this infrequently visited location. However, solely on account of its very small population, the new species should be listed as Endangered: En D ( IUCN 2022). It is noteworthy that C. aetolica and C. corinthiaca (as C. achaia subsp. corinthiaca ) from the C. achaia group as well as additional 16 species and 3 subspecies of Centaurea are included in the Red Data Book of Rare and Threatened Plants of Greece ( Phitos et al. 2009).

Taxonomic comments: —Based on its overall morphology, the new species belongs to a range-restricted, Greek endemic group including Centaurea achaia , C. aetolica , C. corinthiaca and C. euboica Rechinger (1956: 102) , which has been recognized at subsectional rank by some authors viz. C. subsect. Achaia Routsi & Th.Georgiadis in Routsi (1993: 14). Plants of this group are characterized by their pinnatisect to pinnate leaves with lanceolate to linear segments, whitish to purplish florets and convex, stramineous appendages of middle bracts that largely cover the nails of their neighboring bracts on the involucre and are usually armed with stout spines ( Routsi & Georgiadis 1999). The newly described species, Centaurea dolopica , is among the most distinct species in the group, owing to its tall habit with copious and characteristic capitula, which have fewer central florets and smaller (shorter and narrower) involucral bracts than any of the other species. Furthermore, the appendages of the bracts in the new species are not bearing stout spines but rather thin and short ones. Compared to C. achaia ( Fig. 4B,b ), which is the most widespread and morphologically variable species, C. dolopica additionally differs in its denser indumentum—that renders the plants ±greyish,—smaller capitula and shorter achenes. Centaurea aetolica ( Fig. 4D,d ) is sharply distinguished from all other members of the group by its uniformly cream-colored appendages of involucral bracts. The new species differs from C. aetolica in having smaller capitula and lanceolate leaf segments (vs. ±linear). Centaurea corinthiaca sensu stricto ( Fig. 4A,a ) is a very distinct taxon with short stature and capitula with whitish corollas (see Wagenitz & Gamal-Eldin (1985), Routsi (1993)). The involucres of this species are comparable in size to those of C. dolopica ; however, the ratio of the width of bract appendages to the width of the bracts is clearly lower in C. corinthiaca —and the lowest observed in the group— because the bracts are wide with relatively narrow appendages bearing short cilia that cover less the neighboring bracts. Centaurea dolopica is additionally distinguished from C. corinthiaca by its considerably denser indumentum and more branched habit. We, additionally, note that some populations with intermediate characters between C. corinthiaca and C. achaia occur near the locus classicus of the former, and that probably led to the reduction of the Corinthian taxon to the rank of subspecies, viz. C. achaia subsp. corinthiaca Phitos & Georgiadis (1981: 102) , which has been followed to date. However, we suggest that the two species are to be retained separate as discussed below. Lastly, C. euboica ( Fig. 4C,c ), an Euboean endemic species, differs from C. dolopica in being only sparsely hairy and in having ± more attenuate and narrower leaf segments, a less branched habit and larger capitula. The aforementioned morphological differences between the new species and the other members of the group are summarized in Table 2 . We note that the depicted plants of C. dolopica in Figs 1a and 2 represent medium-sized individuals in terms of plant height. The height of medium-sized C. dolopica plants is comparable to large- or very large-sized plants in the rest of the species of the C. achaia group. In the field, we observed some impressive individuals of C. dolopica with up to 40 flowering stems, the largest of those exceeding 1 m in length and each of the stems bearing up to ca. 30 capitula ( Fig. 3A ).

The karyological studies for the genus Centaurea are numerous (see Rice et al. 2015) and have revealed many basic chromosome numbers (x = 8, 9, 10, 11, 12, 13, 14, 15, 16) and several ploidy levels (2x, 3x, 4x, up to 11x) ( Routsi 1993 and references therein). The taxa of C. sect. Acrocentron have also been extensively examined karyologically (e.g., Runemark 1967, Gardou 1969, 1974, Phitos 1970, 1971, Damboldt & Matthäs 1975, Phitos & Georgiadis 1981, Georgiadis & Christodoulakis 1984, Routsi & Georgiadis 1988, 1999, Routsi 1993, Font et al. 2008, Uysal et al. 2009, Ranjbar & Negaresh 2013). These taxa show two basic chromosome numbers, x = 10 and x = 11 ( Routsi 1993, Routsi & Georgiadis 1999). The basic chromosome number x = 11 is considered ancestral and is known only from diploid taxa. Additionally, it has been noted that the number of chromosome counts with x = 11 is more frequent in the eastern than the western Mediterranean region ( Garcia-Jacas & Susanna 1992, Uysal et al. 2009). On the other hand, x = 10 can be observed in both diploids and polyploids reaching up to 2 n = 10x and 2 n = 11x in material of C. spruneri Boiss. & Heldr. in Boissier (1845: 132) ( Phitos 1970, 1971, Phitos & Kamari 1973). Most of the karyotypes belonging to taxa of section Acrocentron consist of metacentric and submetacentric chromosomes as well as satellited chromosomes in many cases ( Routsi 1993, Routsi & Georgiadis 1999). The C. achaia group comprises taxa with x = 11 ( Routsi 1993, Routsi & Georgiadis 1999) including Centaurea dolopica . The karyotype of the new species ( Fig. 5 ) is similar to the karyotypes of the other taxa of C. achaia group ( Routsi 1993, Routsi & Georgiadis 1999). The presence of two pairs of SAT-chromosomes in C. dolopica ’s karyotype has been also observed in the material of C. achaia and C. corinthiaca from Peloponnese and Sterea Hellas, respectively ( Phitos & Georgiadis 1981, Routsi 1993, Routsi & Georgiadis 1999) and also in C. aetolica from Sterea Hellas ( Phitos & Georgiadis 1981). These findings corroborate the inclusion of C. dolopica in the C. achaia group and their close affinities. Moreover, a karyomorphometric study for all taxa related to C. dolopica could be valuable to give a further insight on their relationships.

Phylogenetic analyses revealed the placement of Centaurea dolopica in the Greek-Aegean clade of the C. sect. Acrocentron in close evolutionary relationship with representatives of the C. achaia group ( Fig. 6 ), corroborating the morphological data. Specifically, C. dolopica and C. achaia from its locus classicus in Mt. Chelmos (Peloponnese) form a well-supported clade (bs=82 and pp=0.98; Fig. 6 ) sister to C. aetolica (bs=95 and pp=1; Fig. 6 ). The other species of the C. achaia group, namely C. corinthiaca and C. euboica , together with an individual of C. achaia from the Vilia area in Attica, form another well-supported clade (bs=99 and pp=1; Fig. 6 ) sister to C. ebenoides Moore (1878: 133) ; yet this sister relationship is only moderately supported (bs=76 and pp=0.89; Fig. 6 ). Centaurea ebenoides is a Greek endemic species with a narrow distribution in Euboea and Attica that is morphologically very different from the C. achaia group as it has a short, procumbent habit and very small, inconspicuous bract appendages. Although in the current phylogeny, the C. achaia group is not monophyletic due to the phylogenetic position of C. ebenoides , the incomplete taxon sampling of this study, especially regarding other related species to C. ebenoides , and the moderate support of the sister relationship of C. ebenoides to one of the two well-supported clades of the C. achaia group, cannot confidently reject the monophyly of the C. achaia group. The division of the clade comprising species of the C. achaia group and C. ebenoides into two subclades demonstrates an interesting biogeographic pattern of speciation. Specifically, species diversification in the subclade of C. dolopica , C. achaia (Chelmos) and C. aetolica took place in north Peloponnese, West Greece and East Central Greece, whereas species diversification in the other subclade took place further eastwards, in the areas of Attica and Euboea ( Fig. 7 ). This pattern could suggest the existence of a western and an eastern ancestor in central Greece that diversified allopatrically giving rise to the two aforementioned lineages. Additional taxon sampling and ancestral range estimation analysis in a phylogenetic framework would be required to clarify the biogeographic origins of this clade. Another remarkable finding in this phylogenetic study is the non-monophyletic C. achaia , which raises questions about the species limits. In the most recent circumscription (FoG Web 2022), C. achaia comprises two subspecies, i.e., C. achaia subsp. achaia and C. achaia subsp. corinthiaca . Based on our results, the sample of C. achaia from the locus classicus (Chelmos) and that of C. corinthiaca do not form a monophyletic group but are placed in two different well-supported clades ( Fig. 6 ), thus rejecting the current classification of C. corinthiaca as a subspecies of C. achaia . Furthermore, the sample of C. achaia from Vilia (Attica) is not sister to C. achaia from Chelmos, indicating that this species, even after the exclusion of C. corinthiaca , is nonmonophyletic. Centaurea achaia is the most widely distributed species of the group ( Fig. 7 ) and exhibits the highest morphological variability ( Routsi 1993, Wagenitz & Gamal-Eldin 1985). A more detailed morphological study of C. achaia across its distributional range and an enhanced sampling of different populations of the species in a phylogenetic framework could clarify the species limits of C. achaia and further guide the decision of whether the individuals from Attica should be included in C. corinthiaca or they constitute a different taxon. Species delimitations and relationships in Centaurea are being addressed in an on-going integrative taxonomic study of the genus by the second author that employs morphometric and phylogenomic studies.

Figures

FIGURE 1. Centaurea dolopica. A, habit; B, capitulum; C, marginal (left) and central (right) floret, scale bar = 1 cm; D, two marginal (top left) and three central achenes, scale bar = 5 mm.

FIGURE 2. Holotype of Centaurea dolopica (UPA) mounted on two sheets.

FIGURE 3. Centaurea dolopica plants in their natural habitat: (A) several large plants along a roadside and (B) on a cut slope. (C) Eryngium serbicum in the same habitat.

FIGURE 4. Habits (upper-case letters) and flower-heads on approximate same scale (lower-case letters) of Centaurea sect. Acrocentron representatives from Greece belonging to the C. achaia group; A,a: Centaurea corinthiaca (photos by Katerina Goula); B,b: C. achaia (photos by Katerina Goula); C,c: C. euboica; D,d, C. aetolica; e: C. dolopica.

FIGURE 5. A) Karyotype and B) idiogram of Centaurea dolopica. Arrows indicate satellites.

FIGURE 6. Phylogeny of Centaurea subg. Lopholoma sect. Acrocentron, including the newly described Centaurea dolopica (in bold), with Centaurea subg. Cyanus as outgroup, inferred from Bayesian analysis of the concatenated ITS and ETS sequences. Posterior probabilities (pp) higher than 0.7 and bootstrap values (bs) higher than 50% estimated from MrBayes and RAxML analyses are reported above and below the branches, respectively.At the right, the names of the major clades in C. subg. Lopholoma correspond to those of Font et al.’s (2009) phylogenetic trees.

FIGURE 7. Distribution map of the members of the Centaurea achaia group.