A new species of Centaurea sect. Pseudoseridia (Asteraceae) from north-eastern Turkey

Abstract Centaurea ziganensis Yüzb., M. Bona & İ. Genç, a new species is described and illustrated from Gümüşhane province, NE Turkey. The new species grows in rocky places on the south face of Zigana Mountains, and is closely related to Centaurea drabifolioides, from which it differs mainly in stem, achene and phyllary appendage characters. Micromorphological structures of achenes and karyological features of Centaurea ziganensis and Centaurea drabifolioides were examined in this study.


Introduction
Centaurea L. s.l. is one of the largest and taxonomically most diffi cult genera of the Asteraceae (Dostál 1976). Recent approaches have split this taxon into four genera: Centaurea, Rhaponticoides Vaill., Psephellus Cass. and Cyanus Mill. (Wagenitz and Hellwig 2000, Greuter 2003, Hellwig 2004. Th e genus Centaurea was previously revised by Wagenitz (1975) for the Flora of Turkey and the East Aegean Islands without considering the splitting mentioned above. Even excluding the species now placed in these genera, Turkey is among the richest countries in Centaurea diversity (Wagenitz 1975, Davis et al. 1988, Güner 2000. Recently Centaurea s.l. was revised for Türkiye Bitkileri Listesi by Dural (2012), Ertuğrul (2012) and Uysal (2012aUysal ( , 2012b. According to revised system, the number of known Centaurea species in Turkey is 162 [(excluding 56 species which are now treated within Psephellus (33), Cyanus (16) and Rhaponticoides (7)].
In the Flora of Turkey and the East Aegean Islands (Wagenitz 1975), 34 sections of Centaurea were presented. Some sections of the Turkish Centaurea have been revised, but others, such as sect. Pseudoseridia Wagenitz, have not been revised recently. According to Wagenitz (1975) there were seven Centaurea species in section Pseudoseridia. Since then, six new taxa have been described for the section (Uzunhisarcıklı et al. 2005, Uysal et al. 2007, Aksoy et al. 2008, Bona 2015.
Th e present study is focused on the morphological, micromorphological and karyological criteria for distinguishing a new species in Centaurea sect. Pseudoseridia. Investigations on living and herbarium specimens suggest that this new species is morphologically most similar to C. drabifolioides.

Material and methods
Flowering and fruiting specimens of the C. ziganensis and of related species, C. drabifolioides were collected by the fi rst author several times in 2013 and 2014 from type localities. Th e Centaurea material was examined and compared with material of similar taxa (sect. Pseudoseridia) in ISTE, ISTO, GAZI, ANK, HUB, E, K and G. Th e specimens were also cross-checked with various accounts of Centaurea in relevant fl oras, i.e. Flora Orientalis (Boissier 1875), Flora Europaea (Dostál 1976, Nouvelle Flore du Liban et de la Syrie (Mouterde 1983) and a taxonomic study on Centaurea in Iran (Negaresh et al. 2014). Th e measurements, colors and other details given in the description are based on both herbarium and living materials. Herbarium specimens were deposited in the herbaria of ISTE. Photographs of living material were taken with a Canon D60 digital camera (Canon EF 100 mm macro-lens) and the illustrations of the new species were made by using Adobe Photoshop CS4. Th e morphology of the new species was examined with the aid of a Leica S8AP0 stereo-binocular microscope.
During Scanning Electron Microscopy, 2 mature achenes from C. ziganensis (ISTE 104470) and C. drabifolioides (ISTE 104472) were selected and mounted onto stubs with double-sided adhesive tape, and were then coated with gold. Th e achene surfaces were examined from the lateral sides. For each sample, photographs of the testa were taken using the JEOL JSM-5600 at a magnifi cation 500×, 1000×, and 3000×. Th e terminology of achene characteristics in this work was based on the descriptions used by Stearn (1992), Barthlott (1981), and Koul et al. (2000).
Chromosome number and karyological features of the C. ziganensis and C. drabifolioides, were determined from plant material collected from type localities. All karyological observations were carried out on root tips. Root-tip meristems were provided from achenes by germinating them on wet fi lter paper in petri dishes at room temperature. Firstly, root tips pretreated for 24 h in a-monobromonaphthalene at 4 °C, fi xed in 3:1 absolute alcohol-glacial acetic acid, then the root tips were hydrolyzed with 1 N HCL for 12 min at 60 °C and stained in Feulgen solution and squashed in acetoorcein (Altınordu et al. 2014).
For karyotype analysis, the photographs were taken using OLYMPUS BX53 microscope with camera Kameram12 CCD attachment. Chromosome counts in mitosis metaphase and karyotype analyses were obtained based on three root tips, fi ve metaphase cells for each individual. Measurements of somatic chromosomes were made with the program CAMERAM, they were calculated with formula of the relative variation in chromosome length (CV CL ) (Paszko 2006) and mean centromeric asymmetry (M CA ) according to Peruzzi and Eroğlu (2013). Chromosomes were classified according to the nomenclature of Levan et al. (1964) and Stebbins asymmetry types are given (Stebbins 1971).
Phenology. Centaurea ziganensis fl owers from the end of June to-July, and mature fruits are produced in August−early September.
Etymology. Named after the Zigana Mountains where it was discovered. Distribution and proposed conservation status. As presently known, Centaurea ziganensis is a narrow endemic and known only from the type locality, north eastern Anatolia (Gümüşhane): where the extent of occurrence is less than 100 km 2 (criterion B1), with an estimated area of occupancy of less than 10 km 2 (criterion B2). According to our fi eld observations, habitat destruction through human encroachment such as road construction is the principal threat in the area. Th erefore, on the basis of our knowledge, we argue that the species is potentially Critically Endangered (CR), but more data are needed to estimate its real IUCN category of threat (IUCN 2014).
Karyology. Th e chromosome number of the new taxon is 2n = 18 (Fig 2a). Th e shortest chromosome length is 2.22 μm, the longest is 3.55 μm, and the haploid chromosome length is 24.17 μm. Th e karyotype formula of this taxon consists of 10 median pairs and 8 submedian pairs. Satellites were usually seen on the short arms of the longest sub-metacentric chromosomes. As for karyotype asymmetry, the karyotype of this species is classifi ed according to the symmetry classes of Stebbins as 3A. Intrachromosomal asymmetry (M CA ) is 20.90 and the interchromosomal asymmetry index (CV CL ) is 16.32. Th e karyogram is given in Figure 2b, and ideogram was drawn based on the centromeric index (Fig 2c).
Our study showed that the chromosome number of C. drabifolioides Hub.-Mor. is 2n = 18 (Fig 2d). Th e shortest chromosome length is 1.51 μm, the longest is 2.77 μm, and the haploid chromosome length is 18.64 μm. Th e karyotype formula of this taxon consists of 10 median pairs and 8 submedian pairs. Satellites were usually seen on the  short arms of shortest sub-metacentric chromosomes. As for karyotype asymmetry, the karyotype of this species is classifi ed according to the symmetry classes of Stebbins as 3A. Intrachromosomal asymmetry (M CA ) is 22.71 and the interchromosomal asymmetry index (CV CL ) is 17.95. Th e karyogram is given in Figure 2e, and ideogram was drawn based on the centromeric index (Fig 2f).
SEM observations. Seed surface pattern of Centaurea ziganensis is ruminate. Testa cells are regularly arranged, elongated parallel with the seed surface and the cells are apparently imbricate. Th e cell boundaries are thin and have smooth structure, and the boundaries raised above cell centre (Fig. 3a-c). Even seed surface pattern and testa cell arrangement of C. drabifolioides are similar to Centaurea ziganensis, the cell centres raised above the boundaries and testa cells are not apparently imbricate (Fig. 3d-f). Th e nearly cylindrical involucrum and grey tomentose leaves of C. cheirolepidoides and C. marashica are diff erent from the ovoid to ovoid-oblong involucrum and scabrous leaves of C. drabifolioides and C. yaltirikii. Finally, C. yaltirikii is diff erent with scabrous-barbellate pappus and a widely broad-winged stem (2−4 mm); while C. drabifolioides has scabrous and narrowly winged (0.5−1 mm) stems. In addition, C. drabifolioides has linear-lanceolate leaves compared with the broader and lanceolate, oblong, ovate or oblanceolate cauline leaves of C. yaltirikii.

In section
Achene, pappus and phyllary characters provide the most reliable characteristics to separate Centaurea taxa from each other at sectional and specifi c level (Wagenitz 1975, Wagenitz and Helwig 2000, Bancheva and Gorgorov 2010. It is known that achene micromorphology also provides strong support in the delimitation of Centaurea taxa (Bagheri Shabestari 2013, Bona 2014). C. ziganensis closely related to C. drabifolioides. Even though they both have long pappus, simple, scabrous, decurrent, linear-lanceolate leaves, and are distributed close to each other in a similar habitat, C. ziganensis diff ers from C. drabifolioides in its stem, achene and pappus colour, appendage of phyllary, achene micromorphology and karyology. Th ese two species are compared in Table 1 and Figures 2, 3, 4.
Huber-Morath named C. drabifolioides in 1967, and based his description of this species on plants collected from near Şebinkarahisar (Giresun), NE Turkey. It is not a common plant throughout this range occurs in a relatively small area and has not been recorded from diff erent part of Turkey, it is only known from the type locality. According to type description (Huber-Morath 1967) and Flora of Turkey (Wagenitz 1975) pappus color for C. drabifolioides was indicated as whitish (Huber-Morath 1967) and cream (Aksoy et al. 2008, Uysal et al. 2007). But, the observations we made in the type locality of C. drabifolioides indicate that the pappus color of mature achenes is the same as that of the achene, blackish-chestnut. We think that, the pappus color that is referred to in previous studies was from immature achenes. In this paper, we describe a further new species for Centaurea section Pseudoseridia. Th e total number of sect. Pseudoseridia taxa known from Turkey with this new species, has increased to fourteen, twelve of these are endemic to Turkey. A new identifi cation key for sect. Pseudoseridia in Turkey has been prepared according to Wagenitz (1975), Uzunhisarcıklı et al. (2007) and Bona (2015), and the new species may be inserted as follows: