Acantholimon akaydinii Özüdoğru, sp. nov. (Fig. 1–2)

Type:— TURKEY. Malatya: Darende, around Ayvalı Canyon, steppe, 1200 m, 38.533977 N, 37.643968 E, 30 July 2021, Akaydın 16884, (holotype: HUB!; isotype: ANK!).

Description:— Densely or laxly pulvinate dwarf shrublet. Lower leaves reflexed, leaves triangular-lanceolate, (9)13– 21 (–26) × 0.8–1.2 mm, calcareous punctate, scabridulous on margins. Scapes 2–5 branched, 14–24 cm, distinctly longer than leaves, (3)4–6 scaled; Scales distinctly shorter than internodes, 4–6 mm, aristate, hyaline except vein, calcareous punctate. Inflorescence 9–15 (–20) mm paniculate with 15–40 spikelets, Spikes laxly distichous, 3–10 cm long, with 5–9 spikelets. Spikelets 1-flowered, 8–9.5 mm long. Bracts unequal, glabrous; outer bract herbaceous, 4–5 mm, ovate-triangular, acuminate, broadly hyaline margined; inner bracts subequal 5–6 mm, as long as calyx tube and outer bract, elliptic-lanceolate, acuminate, keeled, hyaline except the vein. Calyx infundibular, 8–8.5 mm long, tube (6–6.5 mm) longer than limb, 10-lobed, lobes truncate-obtuse; veins concolorous, sparsely pilose on the tube and terminating below margin. Petals pink, distinctly longer than calyx.

Eponymy:— This endemic species is named after the Turkish botanist Prof. Dr. Galip Akaydın, who is an expert on the genus Acantholimon, co-supervisor of the first author, and the collector of the holotype.

Distribution, habitat and ecology:— Acantholimon akaydinii is an East Anatolian endemic only known from a small area near Irmaklı Village, Darende, Malatya (Turkey), and belongs to the Irano-Turanian phytogeographical region. It grows on stony and dry calcareous steppes at elevations of 1000–1300 m (Fig. 3), together with Phryna ortegioides (Fisch. & C.A.Mey.) Pax & K.Hoffm., Crataegus monogyn a Jacq., Rhamnus pallasii Fisch. & C.A.Mey., Quercus infectoria Oliv., Inula fragilis Boiss. & Hausskn., Cousinia cataonica Boiss. & Hausskn., Convolvulus compactus Boiss., Jasminum fruticans L., Parietaria judaica L., and Ephedra major Host. subsp. major.

Diagnostic characters:— Acantholimon akaydinii is morphologically most closely related to A. ibrahimii, also from A. sect. Staticopsis, but easily differs by its distinctly longer, much branched scapes and paniculate inflorescence (14–24 mm, 2–5 branched vs. 6–12 mm, 1–2 branched and not paniculate inflorescence), shorter scales (4–6 vs. 7–9 mm), shorter spikelets (8–9.5 vs. 11–12 mm), shorter calyx (8–8.5 vs. 10–11 mm) and pink petals (vs. white) (Table 1.)

Conservation status:— According to current data, A. akaydinii seems to be represented by only one small population in the type locality (nearby Irmaklı village, Darende, Malatya, Turkey). The occupancy area (AOO) of the new species was calculated as smaller than 10 km ², in which <1000 individuals were estimated to occur. The area is under pressure from both agricultural activities and plantations. Considering these facts, in accordance with the B2 ab(i,ii,iii) and C2 a(ii) criteria of the IUCN (2017), the new species is here assessed as “Critically Endangered” (CR).

Other specimens examined (paratypes): — Acantholimon akaydinii: TURKEY, Malatya: Darende, from Irmaklı to Hekimhan, steppe, 1277 m, 28 July 2021, Özüdoğru & Özgişi 5788 (HUB!); Malatya: Darende, Karabacak village, around Ayvalı streams, steppe, Akaydın 16870 (HUB!).

Specimens studied concerning other related species: — Acantholimon ibrahimii Akaydın. — TURKEY. C5 Niğde: Çamardı, Demirkazık village, on calcareous slopes, 1650 m, 08 July 2008, Akaydın 11971 (HUB!).

As shown in Fig. 4, the distribution of the recently described A. ibrahimii which is the closest relative of A. akaydinii, is confined to a limited area around Aladağlar, Niğde, Turkey. This region is part of the Anatolian Diagonal which is one of the most important biogeographical corridors running from the northeast to southwest of Turkey (Davis 1071; Ekim & Güner 1986; Gür 2016; Özüdoğru et al. 2020; Özüdoğru and Mummenhoff 2020; Özüdoğru et al. 2021). The approximate border of this Mountain system has long been known and given in Figure 4. However, precise borders of the Anatolian Diagonal using environmental data such as climate, geology, etc., have not been drawn yet. In any case, the newly described species A. akaydinii is found either in this biological corridor or very close to it. Consequently, the close morphological relationship between A. ibrahimii and A. akaydinii is congruent with their geographical distribution.

Acantholimon akaydinii only grows at 1000–1300 m a.s.l. on the calcareous steppe in Malatya province. The province is one of the regions with the richest flora in Turkey, lying on the Anatolian Diagonal and it comprises 2.075 plant taxa recorded, of which 438 are endemics (Karakuş 2016). This extraordinary plant diversity continues to increase in recent years and several new taxa have been described in this province recently, including Ornithogalum malatyanum Mutlu & Karakuş (2012: 126), Reseda malatyana Yıldırım & Şenol (2014: 1014), Campanula alisankilincii Yıldırım & Şenol (2014: 23), Alkanna malatyana Yıldırım & Şenol (2014: 125), Muscari atillae Yıldırım (2015a: 291), Parietaria semispeluncaria Yıldırım (2015b: 283), Sisymbrium malatyanum Mutlu & Karakuş (2015: 330), Pimpinella enguezekensis Yıldırım, Akalın & Yeşil (2016: 238), Centaurea malatyensis Ş. Kültür & M. Bona (2016: 86), Allium yamadaghensis Yıldırım & Ekşi (2019: 31), A. dönmezii Mutlu & Karakuş (2019: 199), Heldreichia bupleurifolia (Boiss.) (1842: 186) subsp. malatyana Özüdoğru & Yıldırım (2019: 2), etc.

From a morphological point of view, A. akaydinii falls into the group of the Turkish species with laxly distichous spikes and longer scapes, as seen in a revised key provided below. Among these species, A. akaydinii has a unique position because of its paniculate inflorescence.

Finally, with the inclusion of the newly described species, the genus is now represented by 58 species in Turkey.