Polystichum dongchuanense Z.L.Liang, Z.R.He & Li Bing Zhang, 2021

Liang, Zhen-Long, He, Zhao-Rong & Zhang, Li-Bing, 2021, Polystichum dongchuanense and P. menglaense (subg. Haplopolystichum; Dryopteridaceae), two new ferns from Yunnan, China, Phytotaxa 479 (1), pp. 114-120 : 114-117

Polystichum dongchuanense Z.L.Liang, Z.R.He & Li Bing Zhang , sp. nov. ( Figs. 1 & 2 ).

Type:— CHINA. Yunnan: Dongchuan County, Tangdan Town , elev. 1850 m, 26°07’56.43”N, 103°01’44.08”E, in valley under the broadleaved forest, 8 May 2017, Z.- L . Liang , L.- P . Kong , H.- C . Wang & Z.- R . He LZL1293 (holotype PYU!; isotype CDBI!) .

Diagnosis:— Polystichum dongchuanense is most similar to P. acutidens Christ (1902: 59–260) in plant size and pinna size, but the former has oblong-lanceolate pinnae with biserrate margins, and its fertile pinnae have fewer (1–5) sori that are terminal at the upper part of pinnae, whereas the latter has falcate pinnae with serrate margins, and its fertile pinnae have more (18–30) sori that are distributed on whole fertile pinnae.

Plants perennial, evergreen, (35–) 40–45 cm tall. Rhizomes erect, ca. 3 cm long, ca. 1.5 cm in diam., with remnant bases of old petioles; roots dull brown when dried, up to 10 cm long, ca. 0.5 mm in diam. Leaves in tufts; petioles 8– 12.5 cm long, 1.5–2 mm diam, stramineous basal portions covered with scales; proximal petiole scales ovate to ovatelanceolate, 1.5–3 × 1–1.5 mm, papery, dull brown or brown, margins weakly fimbriate, apex acuminate, cells rectangular in the middle, twisted in the margins; distal petiole scales ovate-lanceolate, 0.8–1.2 × 0.4–0.8 mm, membranous, margins weakly fimbriate, apex long-acuminate or caudate. Laminae lanceolate, abaxially dark green, adaxially light green; 1-pinnate, 30–32 cm long, 4–4.6 cm wide, apex acuminate; rachises ca. 1 mm in diam., stramineous, adaxially sulcate; rachis scales ovate or ovate-lanceolate, light brown, up to 1 mm long including tip, 0.5 mm wide at base, margins fimbriate, apex long-caudate; or scales bristle-like, ca 1 mm long, margins entire and fimbriate at base. Pinnae in 28–35 pairs, alternate, separate from each other, 3–5 mm distance, oblong lanceolate, base cuneiform, margins biserrate, apex acuminate, papery, maximal pinnae 2.3–2.5 × 0.5–0.8 cm, basal pinnae narrowing down and basal 1 pair reflexed, largest pinnae located at middle or above middle part of lamina, proximal margins not overlapping rachis, acroscopic and basiscopic margins with cartilaginous, undulate or irregularly toothed, forming a (60–)70–90° angle with rachis, apex acuminate; basal pinnae undulate or entire on margins, obtuse at apex; pinna petioles 0.5–1 mm long; adaxially glabrous; abaxially with microscales; microscales broad-type, ovate or ovate-lanceolate, or lanceolate, whitish brown, 0.5–1(–1.5) mm long, 0.15–0.45 mm wide at base, margins fimbriate; costa sunken adaxially and protruding abaxially, veins obscure and invisible on adaxial side, bulgy and thickened on abaxial side, lateral veins free, forked. All pinnae are fertile excluding 5–8 pairs at base; sori terminal on lateral veins of fertile pinnae, ca. 1 mm in diam., in the middle of the margins and midrib or slightly closer to pinna margins, 1–3 on acroscopic side and 0– 1 on distal basiscopic side, centers 1 mm apart from one another. Indusia peltate, orbicular, margins erose; 64 spores per sporangium, perispores fine-granulate.

Geographical distribution:— Polystichum dongchuanense is only found in Dongchuan Country, Yunnan Province, and may represent an endemic species to Central Yunnan.

Ecology:— Polystichum dongchuanense was observed to grow on limestone rocks under the broad-leaved forest, at an elevation of 1850 m.

IUCN Red List category:—Only one population with about 15 individuals of Polystichum dongchuanense were found in Dongchuan. Based on current information and following the IUCN (The International Union for Conservation of Nature and Natural Resources) guidelines ( IUCN, 2017), this new species should be classified as Critically Endangered (CR).

Etymology:—The species epithet is based on the Chinese pinyin, dongchuan, the county name in central Yunnan, and the Latin suffix -ense, of origin, referring to the type locality and the current known distribution of the species in Dongchuan County, Yunnan. Its Chinese name is suggested as ‘东Lj耳蕨 (dong chuan er jue)’.

Notes:—In addition to the macromorphological distinctness, the perispore ornamentation of Polystichum dongchuanense is fine-granulate and without ridges ( Fig. 1F ), which is quite striking. We did not find any species in the genus whose perispore morphology is known with the same perispore ornamentation ( Huang 1981, Tryon & Tryon 1982, Xiang 1992, Zhang & Kung 1994, Zhang & He 2010, 2011, 2012, Zhang et al. 2010, He & Zhang 2011, 2012, Luo et al. 2012, Han et al. 2016, 2018, Pallawatn et al. 2020). The perispore ornamentation of a number of species in Polystichum is still unknown. It is also little known about the relationships between the perispore ornamentation and phylogeny in the genus.

Figures

FIGURE 1. Polystichum dongchuanense.—A. Habitat.—B. Habit of the plant on the rock.—C. Portion of abaxial lamina.—D. Portion of adaxial lamina.—E. Pinna apex showing sori and indusia.—F. SEM image of spore.

FIGURE 2. Polystichum dongchuanense.—A. Habit.—B. Portion of abaxial lamina.—C. Basal petiole scale.—D, E. Rachis scales (Drawn by Zhen-Long Liang based on the holotype at PYU, scale bar A = 5 cm, B = 2.5 cm, C, D, E = 1 mm).