Polystichum kuankuoshuiense Bo Wang, Q. W. Sun & Li Bing Zhang 2023, sp. nov.

Polystichum kuankuoshuiense Bo Wang, Q.W.Sun & Li Bing Zhang, sp. nov. (Figs. 1–3).

Type: — CHINA. Guizhou Province: Suiyang County, Wangcao Township, Xiashi Village, 28°14′51.2304″N, 107°12′56.79″E, elev. ca. 930 m, 18 June 2018, Bo Wang wb-201806093 (holotype GZTM!; isotypes CDBI!, GZTM!).

Diagnosis: —The new species is very similar to Polystichum auriculum Ching (1949: 309) by having deeply lobed pinnae and a free lobe on each pinna that is lobed to the midrib, but differs from the latter by having a strong and thick rhizome (3–5 cm long, ca. 3 cm in diam.) with numerous proliferous bulbils, bicolorous petiole scales, pinnatipartite pinnae, an acuminate pinna apex, and ca. 15 lobes per pinna; in contrast, P. auriculum has a normal rhizome (<2.5 cm long, ca. 2 cm in diam.) with a few proliferous bulbils, concolorous petiole scales, pinnatilobate or pinnatifid pinnae, a ratio of pinna length to width of <3, an acute pinna apex, and ca. 13 lobes per pinna. Polystichum kuankuoshuiense is also similar to P. bifidum Ching (1958: 245) in having deeply lobed pinnae, a ratio of pinna length to width of ca. 4, an acuminate pinna apex, and ca. 15 lobes per pinna, but differs from the latter in having a strong and thick rhizome with numerous proliferous bulbils; in contrast, P. bifidum has a normal rhizome with few proliferous bulbils, concolorous petiole scales. Polystichum kuankuoshuiense is somewhat similar to P. suiyangense Bo Wang, Q.W.Sun & Li Bing Zhang (2022: 94) in having deeply lobed pinnae and a free lobe on each pinna that is lobed to the midrib, but differs from the latter in having much larger plants and papery and light green lamina with pinnae 18–30 pairs; in contrast, P. suiyangense has much smaller plants, leathery and dark green lamina with pinnae 12–22 pairs. A detailed comparison is available in Table 1.

Description:—Plants perennial, evergreen, 20–40 cm tall. Rhizome erect, slight long, 3–5 cm long, ca. 3 cm in diam. including stipe bases, with base of remnant old petioles, proliferous bulbils sometimes present at base. Roots up to 20 cm long, 2–3 mm in diam. Fronds cespitose, 15–30 per rhizome. Fronds 25–37 cm; petiole 8–12 cm long, 1.5–2 mm in diam. at base, adaxially canaliculate, stramineous, densely covered with scales; scales bicolor, long lanceolate to ovate lanceolate, ca. 3–7 × 0.5–1.2 mm, thickly membranous, margins short serrate, apex acuminate to caudate, luster; scales on distal petiole similar but narrower. Lamina long lanceolate, 12–32 × 3.5–4.5 cm, acuminate-caudate towards apex, slightly contracted towards base, 2.5–3.5 cm wide at base; rachis 1.2–1.5 mm in diam. about middle, stramineous, without proliferous bulbils, adaxially sulcate, sparsely scaly, gradually reduce upwards, scales similar to stipe scales but smaller and narrower; 1-pinnate-pinnatifid. Pinnae 18–30 pairs, 1.8–2.2 × 0.8–1.2 cm, alternate, shortly petiolate, pinnatipartite, light green to green, nearly concolorous on both surfaces, nearly rectangular to long triangular lanceolate, papery, lower pairs obliquely ovate or nearly triangular lanceolate attached almost at right angles to rachis, upper pairs nearly rectangular to long triangular lanceolate, spreading to slightly ascending, acroscopic base auriculate, basiscopic base cuneate, apex acute and terminating with mucronate spine; lobes 6–8 pairs, ascendant, obovate, bases narrowly cuneate, apices 2–4-toothed or no teeth, apices of lobes acute, basal acroscopic lobes obviously larger; adaxially glabrous, abaxially sparsely scaly; microscales light brown, lanceolate to linear-lanceolate, ca. 0.2 × 1.5 mm, margin serrated. Lamina texture papery; venation pinnate, lateral veins dichotomous on auricles and other lobes, distinct or slightly distinct abaxially, indistinct adaxially. Sori small, ca. 1–1.2 mm in diam. when mature, abaxial and terminal on veinlets, nearly medial; indusia present, light brown, entire, evanescent.

Distribution and ecology:— Known only from the type locality at an elevation of ca. 934 m. This population was observed to grow on a karst limestone.

IUCN Red List category: —Following the IUCN Red List Categories and Criteria (IUCN, 2017), Polystichum kuankuoshuiense is assessed as CR (Critically Endangered) based on the fact that only one population with fewer than 20 individuals was found in the field.

Etymology:— Derived from the type locality, Kuankuoshui Nature Reserve (Guizhou, China).

Vernacular name:— AEOiẆąae (kuan kuo shui er jue).

Additional specimens studied (paratypes):— CHINA. Guizhou: Guiyang city, Guizhou University of Traditional Chinese Medicine Germplasm Garden, cultivated (introduced by Bo Wang from the type locality), 18 June 2018, Bo Wang wb-201806088 (CDBI!, GZTM!).