Polystichum deltatum Li Bing Zhang, M.Q.Han & Yan Liu, 2018

Polystichum deltatum Li Bing Zhang, M.Q.Han & Yan Liu View in CoL , sp. nov. ( Figures 1 View FIGURE 1 , 2 View FIGURE 2 )

Type:— CHINA. Yunnan: Mengzi City, Mingjiu Town, Shidong Village, the Stone Cave , alt. 1880 m, 23°29 ′ 21 ″ N, 103°37 ′ 10 ″ E, in a limestone cave, 22 September 2016, Mengqi Han, Yang Dong & Tianfeng Lü HMQ1158 (holotype IBK! GoogleMaps , isotypes CDBI! GoogleMaps , MO! GoogleMaps ).

Diagnosis:— Polystichum deltatum is most similar to P. crassirachis in having toothed upper pinna margins, but the former often has pinnae deltoid and pinna apex acute, while the latter has pinnae deltoid to oblong and pinna apex rounded.

Plants perennial, evergreen, (19–) 30–43 cm tall. Rhizomes ascending, 1.5–2 cm long, ca. 1.5 cm diam., with remnant bases of old petioles; roots dull brown when dried, up to 10 cm long, ca. 0.3 mm diam. Leaves in tufts; petioles 8–14 cm long, ca. 8 mm diam., basal portions covered with scales, scales ovate to ovate-lanceolate, 2–5 × 0.9–2 mm, papery, dull brown, edges with irregular teeth, apex caudate; distal petiole scales similar but narrower, 2.2–4 × 0.5–1 mm, membranous, margins with irregular teeth, apex long-acuminate or caudate. Laminae lanceolate, 1-pinnate, 21–32 × 2.5–3.2 cm, apex acuminate, green when dried; rachises ca. 0.8 mm diam., scales ovate to ovate-lanceolate, dull brown, 1.6–3 mm long including tip, 0.5–0.72 mm wide at base, margins with irregular teeth, apex long-caudate. Pinnae 37–47 pairs, deltoid, (0.9–)1.3–1.6 × 0.5–0.6 cm, lowest 5–8 pairs slightly reduced toward lamina base, basalmost pairs 2/3– 3/4 as large as middle ones, basalmost two pairs 1.4–1.5 cm apart, middle pairs 0.7–0.8 cm apart, all pinnae papery, alternate, not overlapping rachis, basiscopic margins straight or slightly curved, entire, acroscopic margins shallowly crenulate, basiscopic margins forming a 70–85(–90)° angle with rachis, apex acute, base cuneate and asymmetric, acroscopic sides much broader, pinna petiolues ca. 0.3 mm long, auricles acute at apex, abaxially with microscales, microscales broad-type, ovate, ovate-lanceolate or subulate, light brown, 0.2–0.9 mm long, 0.18–0.35 mm wide at base, margins with irregular teeth; adaxially glabrous; veins visible abaxially but somewhat obscure adaxially, lateral veins free, single or forked. Lowest 3–6 pairs of pinnae sterile; sori terminal on lateral veins of fertile pinnae, 1–8 on acroscopic side of fertile pinnae, 0–3 on distal basiscopic side of fertile pinnae, ca. 1 mm diam., closer to pinna margins than to costa (centers of sori 1–1.7 mm from pinna margins, (1–) 1.8–3.3 mm from costa), centers 1.4–1.8 mm apart from one another; indusia rounded, light brown, 1–1.4 mm diam., margins erose. Spores rounded in polar view and elliptic in equatorial view; perispore sculpture cristate with numerous spinules.

Geographical distribution:— Polystichum deltatum is only known from southeastern Yunnan, Southwest China. It is likely endemic to the Stone Cave, Mengzi City.

Ecology:— Polystichum deltatum grows inside a limestone cave at an elevation of 1880 m with humid and shady conditions.

IUCN Red List category:—CR-Critically Endangered following IUCN (2015) Red List criteria: Only one population with about 150 plants was seen in the field.

Etymology:—The species epithet is based on the Latin adjective, deltatum-, deltoid, referring to the often deltoid shape of the pinnae of the species.

Vernacular name:—ḟmNJHẄ(san jiao yu er jue).

Notes:— Polystichum deltatum is a very distinct species and there are no close relatives judging from its morphology.