This new species is similar to Carex calcicola Tang & F.T.Wang, but differs in having culms central (vs. culms lateral), leaf blades 3–5.5 mm wide (vs. 7–15 mm wide), bracts longer than spikes (vs. shorter than spikes or nearly equal in length), utricles 4–5 mm long (vs. 5.5–6.5 mm long), shorter, and nutlets abruptly contracted into an erect beak at apex (vs. curved or coiled beak at apex).

China. Guangxi: Du’an County, National Geopark in Dongmiao Town, 23°59'41"N, 107°59'14"E, limestone slope, alt. 240 m, 5 May 2021, W. B. Xu, C. R. Lin & Z. C. Lu 14641 (holotype: IBK! barcode IBK00457898; isotypes: IBK! barcode IBK00457899, ZJFC!).

Perennial herbs. Rhizomes short, woody, thick. Culms central, caespitose, 20–50 cm tall, trigonous, slightly scabrous, base with dark brown fibrous sheaths. Leaves longer than culms; blades 3–5.5 mm wide, leathery, margin slightly involuted, scabrous on margins and abaxial leaf surfaces. Bracts leaf-like, longer than spikes, sheathed; sheaths 10–30 mm long. Spikes 3–6; terminal spike staminate, clavate-cylindrical, 3–7 cm long, 2–3 mm wide, base with a 1.5–2.5 cm long peduncle; lateral spikes androgynous, rarely pistillate, cylindrical, 3–5(–8) cm long, 5–7 mm wide, staminate part 1–3 cm long, densely flowered, pistillate part 1.5–4 cm long, sparsely flowered, base with a 1–5 cm long peduncle; peduncles enclosed or slightly exserted from bract sheaths. Staminate glumes oblong-lanceolate, 4–5.5 mm long, yellow-brown, obtuse or acuminate at apex, pale yellow-brown 3-veined dorsal costa. Pistillate glumes (basal part) broadly ovate, ca. 4 mm long, yellow-white, acuminate at apex, yellow 3-veined dorsal costa excurrent into a scabrous awn, middle and upper ones ovate, 3–3.5 mm long, yellow-white, acuminate at apex, yellow 3-veined dorsal costa excurrent into a 0.5–1 mm long scabrous awn. Utricles yellow-green, ovoid (excluding beak), obtusely trigonous, 4–5 mm long (including beak), longer than pistillate glumes, chartaceous, distinctly thinly veined, glabrous, base cuneate, apex gradually contracted into a 2–2.2 mm long beak, orifice 2-lobed with short teeth. Nutlets tightly enveloped, rhombic-ovoid, trigonous, castaneous, 2.5–3 mm long, with 3 angles constricted at middle, sides concave above and below, base with a curved stipe, apex abruptly contracted into a ca. 1 mm long beak, beak erect or slightly curved, annulate at orifice; style thickened at base; stigmas 3.

The specific epithet ‘duanensis’ refers to the type locality of this new species.

Flowering and fruiting mid-March to early May.

Carex duanensis has only been collected from limestone areas of Guangxi, China. It is currently known to grow sporadically in forests or shrubs on limestone slopes, at an elevation of 200–500 m.

(paratypes). China. Guangxi: Du’an County, National Geopark in Dongmiao Town, 23°59'41"N, 107°59'14"E, limestone slope, alt. 240 m, 5 May 2021, W. B. Xu, C. R. Lin & Z. C. Lu 14640 (IBK!, ZJFC!); the same locality, 5 May 2021, W. B. Xu, C. R. Lin & Z. C. Lu 14642 (IBK!, ZJFC!); Nongshui, Yu’an Village of Dongmiao Town, 23°57'47.37"N, 107°56'39.37"E, in limestone thickets slope, alt. 290 m, 13 March 2023, W. B. Xu, C. R. Lin, Z. C. Lu & J. Q. Huang 15556 (IBK!); Nongyi, Ditong Village of Dongmiao Town, 23°58'51.52"N, 107°52'06.17"E, in limestone slope, alt. 465 m, 13 March 2023, W. B. Xu, C. R. Lin, Z. C. Lu & J. Q. Huang 15579 (IBK!); Yizhou City, Latan Village of Anma Town, 24°42'14"N, 108°28'07"E, under limestone forests, alt. 250 m, 1 May 2021, W. B. Xu, C. R. Lin & Z. C. Lu 14459 (IBK!).

The new species has been found in three localities in Du’an County and one locality in Yizhou City, Guangxi, China. One locality is in Du’an County, National Geopark in Dongmiao Town, two localities are in the assessment area of Southwest Karst National Park, which is currently being prepared; the populations are in protected areas where they are less threatened. According to the IUCN Red List Categories and Criteria (IUCN 2022), Carex duanensis will be considered in the Least Concern (LC) category.

SEM micromorphology uses detailed descriptions which are shown in Figs 1, 2. The utricles of Carex duanensis and C. calcicola are both obovoid, glabrous, with many longitudinal veins; beak margins prickly-hairy, and short and sharp 2-teethed at the top (Fig. 3), but the utricle length of C. duanensis is slightly shorter than those of C. calcicola. The nutlet shapes of C. duanensis and C. calcicola are both rhombic-ovoid, with 3 angles constricted at middle and epidermal cells 5- or 6-gonal, rarely 4-gonal, with straight anticlinal walls and solitary rarely 2 silica bodies. The nutlet beak of C. duanensis is erect, whereas that of C. calcicola is curved (Fig. 4).

Figure 1. 

Carex duanensis sp. nov. A habit B lateral spikes C utricles D nutlets E pistillate glumes of middle and upper part F staminate glumes.

Figure 2. 

Carex duanensis sp. nov. A habit B staminate glume C pistillate glume of basal part D, E pistillate glumes of middle and upper part F utricle G nutlet. (Drawn by Xiao-Feng Jin; based on the holotype: W.B.Xu et al. 14641 in IBK).

Figure 3. 

SEM micromorphology of utricles of Carex duanensis (A–C) and C. calcicola (D–F) A, D overview B, E surface C, F beak . Scale bars: 1 mm (A, D); 200 μm (B, C, E, F)

Figure 4. 

SEM micromorphology of nutlets of Carex duanensis (A, B) and C. calcicola (C, D) A, C overview B, D surface, Scale bar: 1 mm (A, C); 50 μm (B, D)

Carex duanensis has nutlets rhombic-ovoid, obtusely trigonous, with 3 angles constricted at middle, sides concave above and below, apex abruptly contracted into a ca. 1 mm long beak, beak erect or slightly curved, annulate at orifice. Based on these morphological characters, C. duanensis belongs to C. sect. Rhomboidales and is similar to C. calcicola (Dai et al. 2010), but differs from the latter in having culms central, leaf blades 3–5.5 mm wide, bracts longer than spikes, utricles 4–5 mm long, shorter, and nutlets abruptly contracted into an erect beak at apex. The morphological differences of C. duanensis and C. calcicola are shown in Table 1.