Polystichum arcuatum Li Bing Zhang, M.Q.Han & Yan Liu, 2016

Han, Meng-Qi, Liu, Yan & Zhang, Li-Bing, 2016, Seven new species of Polystichum (subg. Haplopolystichum; Dryopteridaceae) from southern China, Phytotaxa 280 (3), pp. 201-221 : 203-204

Polystichum arcuatum Li Bing Zhang, M.Q.Han & Yan Liu , sp. nov. ( Figures 1 , 2 )

Type:— CHINA. Guizhou:Anshun City, Longgong Town, Erpo Village, elev. 1210 m, 26°02 ′ 15 ″ N, 105°49 ′ 18 ″ E, inside a limestone cave, 23 May 2015, Mengqi Han & Jinquan Huang HMQ463 (holotype IBK!, isotypes CDBI!, MO!).

Diagnosis:— Polystichum arcuatum is most similar to P. deltodon ( Baker 1880: 494) Diels (1899: 191) in having similar size of pinnae and marginal sori, but the former has oblong-deltoid pinnae with strongly curved (like a bow) basiscopic pinna margins, while the latter has oblong pinnae with straight basiscopic pinna margins.

Plants perennial, evergreen, 34–44 cm tall. Rhizomes ascending, 1.2–1.8 cm long, ca. 1.4 cm diam., with remnant bases of old stipes; roots dull brown when dried, 3–6 cm long, ca. 0.3 mm diam. Leaves in tufts, 9–14 per rhizome; petioles 5–8 cm long, 0.6–0.8 mm diam., basal portions densely covered with scales, scales broad-lanceolate to ovate-lanceolate, 3–4 × 1–1.5 mm, papery, dull brown, edges with lighter color and almost entire, apex acuminate; distal petiole scales similar but narrower, 1.4–2.4 × 0.4–0.7 mm, membranous, margins irregularly erose or short-ciliate, apex long-acuminate or caudate. Laminae lanceolate, 1-pinnate, 24–27 × 2.2–2.7 cm, apex acuminate, green when dried; rachises 0.7–1 mm diam., scales lanceolate to ovate-lanceolate, dull brown, 1.1–1.5 mm long including tip, 0.4–0.6 mm wide at base, margins sparsely ciliate, apex long-caudate. Pinnae 30–38 pairs, deltoid, 0.8–1.4 × 0.3–0.4 cm, basalmost 0–2 pairs slightly smaller, ca. 2/3 to same size as middle ones, 1.4–1.5 cm apart, middle pairs 0.6–1 cm apart, all pinnae papery, alternate, basiscopic margins entire, acroscopic margins almost entire or very shallowly crenulated, basiscopic margins forming a 60–120° angle with rachis, apex acute, base cuneate and asymmetric with acroscopic sides being much broader, petioles 0.3–0.5 mm long, abaxially with microscales, microscales lanceolate, brown, 0.3–1.5 mm long, 0.1–0.2 mm wide at base, margins with irregular outgrowths; adaxially glabrous; veins visible abaxially but somewhat obscure adaxially, lateral veins free, single or forked. Lower 1–4 pairs of pinnae sterile; sori terminal on lateral veins of fertile pinnae, (1–)3–7 on acroscopic side of fertile pinnae, 0–1 on distal basiscopic side of fertile pinnae, 1–1.2 mm diam., closer to pinna margins than to midrib (centers of sori 1–1.4 mm from pinna margins, 1–5 mm from midrib), centers 1–1.5 mm apart from one another; indusia rounded, ca. 1 mm diam., nearly entire. Spores rounded in polar view and elliptic in equatorial view; perispore sculpture cristate with numerous spinules.

Geographical distribution:— Polystichum arcuatum is only known from central Guizhou, China. It is likely to occur only in the type locality.

Ecology:— Polystichum arcuatum grows inside a limestone cave at an elevation of 1210 m with humid and shady conditions.

IUCN Red List category:—CR-Critically Endangered: Only one population with about 100 plants was seen in the field.

Etymology:—The species epithet is based on the Latin, arcuatum , bow-curved, referring to the shape of the basiscopic pinna margins of the species.

Taxonomic notes:— Polystichum arcuatum stands out in P. subg. Haplopolystichum by having strongly curved (like a bow) basiscopic pinna margins. The ratio of the length to width of pinnae is smaller than that in most species of P. subg. Haplopolystichum. Its lower pinnae are not or only slightly narrowed toward the base of rachis. The pinnae are deltoid-oblong, unlike most species in the subgenus that have either deltoid or oblong pinnae. A preliminary molecular analysis failed to identify its most closely related species.

Figures

FIGURE 1. Polystichum arcuatum.—A. Inside view of the sinkole where the new species was discovered.—B. Habitat and plant.—C. Portion of abaxial lamina.—D. Habit.—E. Lower portion of plant.—F. Portion of abaxial lamina bearing sori.—G. Portion of pinna showing sori.—H. Equatorial view of spore under SEM.—I. Polar view of spore under SEM.

FIGURE 2. Polystichum arcuatum.—A. Habit.—B. Portion of abaxial lamina.