Centaurea gigantea subsp. davisii (Asteraceae, Cardueae-Centaureinae), a new subspecies from SE Turkey

Introduction

Centaurea L. s. l. (Cardueae, Asteraceae) with about 400–700 species depending on the taxonomic treatment, is the largest genus in the subtribe Centaureinae (Wagenitz, 1975; Bremer, 1994; Wagenitz & Hellwig, 1996, 2000; Hellwig, 2004; Garcia-Jacas et al., 2006; Susanna & Garcia-Jacas, 2007; Negaresh, 2018). The main distinguishing characters of Centaurea are the presence of scarious appendages on phyllaries, lateral areole at achene insertion, and sterile peripheral florets lacking staminodes (Dittrich, 1977; Wagenitz & Hellwig, 1996; Negaresh, 2020). Centaurea is well represented in the Mediterranean and Irano-Turanian floras (Hellwig, 2004; Susanna & Garcia-Jacas, 2009; López et al., 2011; Negaresh, 2025). Considering the area of its distribution along with the high number of species assigned to it, the taxonomic delineation of Centaurea has been obscure (Garcia-Jacas et al., 2001). Currently it is clear that the traditional Centaurea was polyphyletic, and it has been divided into the putatively monophyletic genera Centaurea s. str., Rhaponticoides Vaill., Psephellus Cass. and Cyanus Mill. (Wagenitz & Hellwig, 2000; Greuter, 2003; Hellwig, 2004; Susanna & Garcia-Jacas, 2007, 2009). In Turkey, the genus is currently represented by 220 species in 33 sections (Wagenitz, 1975; Negaresh et al., 2015; Oreizi et al., 2017; Hamzaoğlu & Koç, 2020; Duman et al., 2021; Özbek, 2021; Uysal et al., 2024). Centaurea sect. Cynaroides Boiss. with 18 species, 3 subspecies and 2 varieties is one of the largest sections of the genus in Turkey (Negaresh & Rahiminejad, 2018). A considerable number of taxa (13 species and 2 subspecies) are endemic to the country (Negaresh & Rahiminejad, 2018). Members of this section differ from those in the other sections by their large habit, capitula arranged in a spike-like or raceme-like inflorescence, and especially by entire hastate leaves (Negaresh et al., 2014, 2015). During our recent revision of herbarium sheets of C. sect. Cynaroides deposited in the E herbarium, we found one specimen (E00476321) that resembled C. gigantea Schultz-Bip. ex Boiss., yet differed in certain morphological characters. This specimen was annotated as new for Turkey by Wagenitz but was never published. In 2019, the second author collected some specimens from the same area from where the E herbarium specimen was collected. After a thorough examination of relevant taxonomic literature and comparison with numerous specimens deposited in different herbaria, we concluded that the E specimen (E00476321) as well as those collected in the same area by the second author, in fact represent a subspecies new to science. Therefore, we decided to describe these specimens as a new subspecies, i.e., C. gigantea subsp. davisii Negaresh.

Materials and methods

A total of 510 specimens including 30 samples specifically collected for this study and 480 herbarium sheets kept in the herbaria B, BASU, BC, BEI, BM, BRA, C, E, EGE, FI, FUMH, G, G-BOIS, GAZI, GB, GOET, HAL, Hb. Hub.-Mor., HSB, HUI, HUJ, IRAN, ISTE, JE, K, KHAU, LAU, LD, M, MO, N, P, PR, RUH, S, SAV, TARI, VAN, W, WAG, WU, and Z+ZT (all herbarium codes according to Thiers 2025) were examined in this investigation. Digitized specimens were obtained upon request from the relevant herbaria and viewed via their online herbarium catalogues of the herbaria or via JSTOR (2023). For a detailed perspective of using morphology and applying these characters in the treatment of this genus, we conducted a thorough review of the taxonomic aspects of Centaurea sect. Cynaroides (Wagenitz, 1975, 1980, 2006, 2019; Ranjbar et al., 2013; Ranjbar & Negaresh, 2014a, 2014b; Negaresh & Rahiminejad, 2014, 2016, 2018). Morphological characters such as length of habit, ramification of stems, indumentum of all parts, shape, length, dissection and decurrence of leaves, number and arrangement of capitula, length of peduncles, shape and size of involucres, shape, size, texture and indumentum of phyllaries, shape, size, color, status and concealing of appendages, number, length and shape of cilia, texture and length of spines, color of flowers, length of central florets, visibility and number of peripheral florets, size, shape and color of achenes, and shape, length and color of pappus etc., were studied in every taxon. The taxonomic applicability of these characters was evaluated among all the material studied. All vegetative and floral parts were measured in a dry state and some parts were observed and measured under a stereomicroscope.

Results and discussion

Centaurea gigantea Schultz-Bip. ex Boiss. subsp. davisii Negaresh, subsp. nov. Figures 1 and 2.

Diagnosis: Centaurea gigantea subsp. davisii is related to C. gigantea subsp. gigantea, from which it differs mainly in its phyllaries indumentum gray-lanate-floccose (vs. tomentose), flowers yellow (vs. purple or pink), anthers pale yellow (vs. deep purple), peripheral florets shorter than central ones, slightly conspicuous, 4-lobed, limb lobes filiform (vs. longer than central ones, distantly conspicuous, 5-lobed, limb lobes linear).

Description: Biennial plants, all plant usually pale green, with a thick turnip-like root, 85-100 cm tall; collar of fibrous petiolar remains present at stem base. Stem erect, simple, 5-8 mm in diameter at base, cylindrical, with thick yellowish striations, densely covered with long hirsute-articulate and sessile gland hairs. Leaves rigid, papyraceous (on drying), undivided, loosely covered with hirsute-articulate and sessile gland hairs, denser along midrib and veins, sometimes upper ones mixed with arachnoid hairs. Basal and lower cauline leaves petiolate, simple, usually withered at anthesis, broadly ovate, lamina 10-12 × 7-10 cm, petiole 10-15 cm long, margins denticulate, acute at apex. Median cauline leaves sessile, simple, oblong or lanceolate, 15-20 × 3-8 cm, broadly decurrent, up to 55 mm along stem, margins scabrous, acuminate at apex. Upper cauline leaves increasingly smaller, sessile, lanceolate to narrowly lanceolate, 4-7 × 0.8-1.1 cm, broadly decurrent or winged, entire, elongate into a mucro at apex. Capitula numerous, 7 to 13(-15), arranged in a raceme, peduncles short or pedunculate in the upper part, gradually longer towards base. Involucres subglobose to obconical, truncate at base, gradually contracted at apex, 30-35 × 25-30 mm. Phyllaries multiseriate, coriaceous, imbricate, grayish, densely gray-lanate-floccose. Appendages firm, concealing part of phyllaries only, mostly straw-coloured, the inner ones pale brown, elongate triangular, 2.8-3 mm wide at base (excluding cilia), gradually narrowed into a spine 7-12 mm long; cilia several, ± patent, 5-7 on each side, 2.5-5 mm long. Outer phyllaries ovate, 5-7 × 5-7 mm, appendages 8-12 × 10-13 mm (including cilia and spine). Median phyllaries oblong or lanceolate, 10-14 × 8-10 mm, appendages 15-20 × 12-15 mm (including cilia and spine). Inner phyllaries lanceolate-linear or linear, 20-25 × 5-10 mm, appendages 10-16 × 3-6 mm (including cilia and spine), sometimes lacerate. Flowers yellow; central florets hermaphroditic, 35-37 mm long, corolla 13-14 mm long, 5-lobed, lobes 6-7 mm long, with deep yellow nerves, anthers pale yellow, longer than corolla, with apical appendages acute, stigma exserted from corolla up to 4 mm; peripheral florets sterile, shorter than central ones, numerous (15-20 in each capitulum) and slightly conspicuous, finely dissected, not radiant, 4-lobed, limb lobes filiform, 5-6 mm long. Achenes oblong, ca. 6 mm long, ca. 3 mm wide, yellowish to silver-bronze, smooth and shiny, glabrous; insertion areole lateral, yellow, 0.8-1 mm long. Pappus double, persistent, multiseriate, brownish, scabrous, 6-7 mm long, bristles of inner rows much shorter than others.

Type: Turkey. C9 Hakkari: Çölemerik, 1700 m, 17 August 1954, Davis 24514 (holotype: E00476321, isotype: K00210960!). Paratypes: Turkey. Hakkari: Çölemerik, 1300-1400 m, 19 July 2019, Kaya 698 (KHAU!); Kaya 988 (KHAU!).

Etymology: The subspecific epithet is given in honour of Dr. Peter H. Davis who collected the type specimens of subspecies.

Figure 1. Holotype of Centaurea gigantea subsp. davisii (E00476321).

Figure 2. Paratype of Centaurea gigantea subsp. davisii (photo provided by Zafer Kaya). A: habit; B: close-up of capitulum; C: close-up of achene with pappus. Scale bars: A = 5 cm, B = 1 cm, C = 4 mm.

Distribution and habitat: Centaurea gigantea subsp. davisii is a rare endemic found in Hakkari province, SE Turkey (Figure 3). It represents the Irano-Turanian floristic element, and grows on roadside slopes, Quercus forest, and mid-montane zones, at elevations of 1300-1700 m a.s.l. (Figure 3).

Figure 3. Distribution of Centaurea gigantea subsp. davisii (circle), C. gigantea subsp. gigantea (squares), and C. gigantea subsp. rechingeri (triangles).

Conservation status: Centaurea gigantea subsp. davisii is known only from the type locality. After detailed field investigations, no other population were found in the surrounding area. The only known population covers an area of ca. 1000 m² and consists of ca. 100 individuals. Possible threats include habitat deterioration (erosion), proximity to human settlements, and restricted distribution. According to the IUCN Red List categories and criteria (IUCN, 2012), Centaurea gigantea subsp. davisii should be considered ‘Critically Endangered’ (CR) [criterion B2ab].

Taxonomic remarks: Centaurea gigantea generally occurs in Arbil, Dohuk, Kirkuk, Mosul and Sulaymaniyah provinces, from N to NE Iraq and there are also a few populations in Hakkari province, SE Turkey (Figure 3). Centaurea gigantea belongs to C. sect. Cynaroides, which includes taxa with racemose or dichasial synflorescences, decurrent upper cauline leaves, ovoid to subglobose involucres, triangular to ovate or orbicular appendages, not decurrent, and usually ciliate and ending in a firm spine or spinule, and with pink, purple or yellow flowers (Negaresh & Rahiminejad, 2018). It is represented by two subspecies (Negaresh & Rahiminejad, 2018): subsp. gigantea has involucres 30-35 × (20-)25-30 mm, appendages elongate triangular, spine 5-13 mm long, pappus 8-10 mm long (Figure 4); and subsp. rechingeri Negaresh, which endemic to NE Iraq, has involucres ca. 45 × 45 mm, appendages shortly triangular, spine 2-5 mm long, pappus ca. 13 mm long (Figure 5). Centaurea gigantea subsp. davisii is distinguished from both subspecies by having phyllaries indumentum gray-lanate-floccose, flowers yellow, peripheral florets shorter than central ones and slightly conspicuous, limb lobes filiform (Table 1). This subspecies is also related to C. spicata Boiss., which is found in S Turkey and NW Syria, in its indumentum of stem and leaves, shape of median and upper cauline leaves, and shape of inflorescence. However, it differs from C. spicata by its basal and lower cauline leaves undivided, broadly ovate, lamina 10-12 × 7-10 cm (vs. lyrate, broadly triangular to lanceolate, lamina 6-16 × 6-28 cm), involucres subglobose to obconical, gradually contracted at apex, 30-35 × 25-30 mm (vs. ovoid, 25-28(-32) × (17-)20-25 mm), appendages straw-coloured or brown, elongate triangular, 2.8-3 mm wide at base (excluding cilia) (vs. ovate-lanceolate to narrowly triangular, sometimes lanceolate-triangular, brown, rarely straw-coloured, (3-)4-6 mm wide at base (excluding cilia)), cilia 5-7 (vs. 7-10) on each side, flowers yellow, 35-37 mm long (vs. purple, 28-32 mm long), and also achenes ca. 6 mm (vs. 4-5 mm) long. In addition, C. gigantea subsp. davisii shares some characters such as leaves undivided, involucres size 30--35 × 20--25 mm and a racemose inflorescence with C. daneshvarii Negaresh, which is endemic to W Iran, but differs from it by its basal leaves broadly ovate (vs. lanceolate), median cauline leaves 15-20 × 3-8 cm, broadly decurrent, up to 55 mm along stem (vs. 6-8 × 1.5-2 cm, decurrent, up to 15 mm along stem), upper cauline leaves 4-7 × 0.8-1.1 cm, broadly decurrent or winged (vs. 6-8 × 1.5-2 cm, decurrent, up to 15 mm along stem), appendages elongate triangular, 6-12 mm long (vs. triangular, 2-7 mm long), flowers yellow, 35-37 mm long (vs. pink, 38-40 mm long), peripheral florets shorter than central ones, numerous (15-20 in each capitulum), slightly conspicuous, 4-lobed (vs. much shorter than central ones, few (3-5 in each capitulum), very inconspicuous, 3-lobed), achenes ca. 6 mm (vs. 7-7.5 mm) long, and also pappus 6-7 mm long, bristles of inner rows much shorter than others (vs. 14-15 mm long, bristles of inner rows slightly longer than others).

Figure 4. Centaurea gigantea subsp. gigantea in the field of Turkey (photo provided by Zafer Kaya). A: habit; B: close-up of capitulum. Scale bars: A = 2 cm, B = 1 cm.

Figure 5. Holotype of Centaurea gigantea subsp. rechingeri (W1960-0009727).

Table 1. Diagnostic morphological characters of Centaurea gigantea subsp. davisii and C. gigantea subsp. gigantea.

Key to the subspecies of C. gigantea

1. Phyllaries indumentum gray-lanate-floccose; flowers yellow; anthers pale yellow; peripheral florets shorter than central ones, slightly conspicuous, 4-lobed, limb lobes filiform ………………………….………………………………. C. gigantea subsp. davisii

– Phyllaries indumentum tomentose; flowers purple or pink; anthers deep purple; peripheral florets longer central ones, distantly conspicuous, 5-lobed, limb lobes linear ……………………………………………………………………………...….………..……. 2

2. Involucres 30-35 × (20-)25-30 mm; appendages elongate triangular; spine 5-13 mm long; pappus 8-10 mm long ………………………………………………………………………………………………….…………... C. gigantea subsp. gigantea

– Involucres ca. 45 × 45 mm; appendages shortly triangular; spine 2-5 mm long; pappus ca. 13 mm long ……………………………………………………………………………………………….……..…….. C. gigantea subsp. rechingeri

Selected specimens examined: Centaurea gigantea subsp. gigantea. Iraq. Arbil province: Handren mountains near Rawanduz, 1300 m, 23 June 1893, Bornmüller 1490 (B!); in montibus between Arbil and Rawanduz, 700 m, Bornmüller 1491 (B!); between Dokan and Mirza Rustam, 1200 m, 28 July 1957, Rechinger 10988 (W!); Chiya-I Mandau prope Walash, 1050 m, Guest 2673 (K!); between Dargala and Karoukh, 12 June 1959, Rawi et al. 27734 (K!). Sulaymaniyah province: between Sulaymaniyah and Dokan, 700 m, Rechinger 12482 (W!); between Sulaymaniyah and Qara Dagh, 24 June 1957, Haines 1314 (E!, K!); Qara Dagh, 1500 m, 9 August 1957, Haines 1244 (E!). Kirkuk province: E Chamchamal, Rechinger 10061 (W!); on Dukan highway, 20 km NW of Sulaimaniya, 760-780 m, 14 June 1957, Rawi 21720 (K!). Mosul province: 18 km E Duhok toward Amadiyah, 800 m, 10-12 July 1957, Rechinger 11531 (B!, K!); Suwara Tuka, in apertis quercetorum, 1200 m, 1956, Rechinger 15817 (E!); in faucibus Mazurka prope Amadiyah, 1500 m, Guest 15817 (K!); in apricis lapidosis ad pagum Gara Kurdistaniae prope Mossul, 1 August, 1841, Kotschy 349 (E!, FI!, G!, GOET!, HAL!, K!, LAU!, M!, MO!, P!, S!, WAG!, W!). Dohuk province: 19 km E of Dohuk, Rechinger 45976 (W!); Ser Amadiya, 1450 m, 13 July 1976, Al-Dabbagh et al. 45976 (K!); Sarsang, Haines W1244 (K!). Turkey. Hakkari province: Semdinli Yüksekova aras, 1840 m, 29 July 1978, Baytop et al. 41318 (ISTE!); inter Yüksekova et Bagashli, 1880 m, 23 July 1974, Rechinger 49883 (K!); gever plain, 1845 m, 18 June 2019, Kaya 697 (KHAU!); Kaya 986 (KHAU!); Kaya 987 (KHAU!). Centaurea gigantea subsp. rechingeri. Iraq. Arbil province: Qandil mountains between Shahidan and Pushtashan, 1000 m, 28 July 1957, Rechinger 11013 (K!, W!); 4-9 km W Raoia, 550 m, Rawi & Serhang 23756 (K!); Kaiwa, 670 m, 27 July 1957, Rawi & Serhang 23756 (K!); Karoukh, N of Shahidan, 1000 m, 28 July 1957, Rawi & Serhang 23801 (K!).

Acknowledgements

We are grateful to the personnel of the following herbaria: B, BASU, BC, BEI, BM, BRA, C, E, EGE, FI, FUMH, G, G-BOIS, GAZI, GB, GOET, HAL, Hb. Hub.-Mor., HSB, HUI, HUJ, IRAN, ISTE, JE, K, KHAU, LAU, LD, M, MO, N, P, PR, RUH, S, SAV, TARI, VAN, W, WAG, WU, and Z+ZT, for their contributions during the revision of the material and for providing images of the type specimens. We would also like to thank the Agricultural Sciences and Natural Resources University of Khuzestan (project no. 1403/04) for financial support.