Polystichum pseudodangii Li Bing Zhang, N.T.Lu & Liang Zhang, 2023

Lu, Ngan Thi, Zhang, Liang, Thanh, Nguyen Trung, Toan, Le Chi & Zhang, Li-Bing, 2023, Three new species and one new record of the fern genus Polystichum (Dryopteridaceae) from Vietnam, Phytotaxa 607 (1), pp. 85-94 : 86

Polystichum pseudodangii Li Bing Zhang, N.T.Lu & Liang Zhang , sp. nov. ( Fig. 1 ).

Type:— VIETNAM. Ha Giang Province: Quan Ba District, Nghia Thuan Commune, Bat Dai Son Nature Reserve , elev. ca. 1260 m, 23° 7’57.41” N, 104°55’43.89” E, 10 December 2013, limestone mountain, Li Bing Zhang, Liang Zhang & Ngan T. Lu 6891 (holotype VNMN!; isotypes CDBI!, MO!) .

Diagnosis:— This species is most similar to Polystichum dangii P.S.Wang in Wang & Wang (2001: 531) in having oblong and coriaceous pinnae with entire margins and rounded apex and sori close to pinna margin, but the former has blackish petiole scales, longer frond (up to 38 cm), pinnae attached at 70° (–90°) angles to rachis, more pairs of pinnae (22–29 pairs) per lamina, auriculate pinnae, and sori above the midrib up to 10 pieces, whereas the latter has brown petiole scales, shorter frond (up to 22 cm), pinnae attached at 120° (–140°) angles to rachis, fewer pairs of pinnae (5–21 pairs) per lamina, exauriculate pinnae, and sori above the midrib up to 4 pieces.

Plants medium-sized, evergreen, 23–30 cm tall. Rhizomes erect, ca. 1 cm in diam.; roots blackish when dried, up to 15 cm long, ca. 0.4 mm in diam. Fronds 11–15 per rhizome; stipe brown, 4–11 cm long, ca. 0.7 mm in diam., basal stipe scales brown, lanceolate (or ovate-lanceolate), 1.5–1.7 × 6.0–8.0 mm, thin papery, brown, margins entire, apex acuminate, twisted in the margins; distal petiole scales subulate, lanceolate, 0.3–0.7 × 0.8–5.0 mm, membranous, margins irregular dentate, apex long-acuminate. Laminae 1-pinnate, lanceolate, 2.8–3.5 × 17–27 cm, apex acuminate; rachises ca. 1 mm in diam., stramineous, adaxially sulcate, sparsely scaly; abaxially densely scaly; scales appressed, subulate with rounded base, brown to light brown at the base, dark brown at the apices, long acuminate, margin dentate at base, irregular dentate at distal part. Pinnae in 22–29 pairs, alternate, or sometimes opposite at base, attached at 70° (–90°) angles to rachis, separate or overlapped by auriculate, rarely imbricate, 0.7–1.3 cm distant (from attached point), acroscopic blunt auriculate; basal pinnae broadly oblong to obliquely oblong, 0.6–1.0 × 1.1–1.5 mm, sessile, 2 basal pairs up to 1.3 cm apart, apices of obtuse, sometimes obtuse-rounded, broadly acute, bases obviously asymmetrical, acroscopic base with auricles, apex of auricles acute, margin entire; middle pinnae longest, oblong to slightly oblong, 0.4–0.7 × 1.2–1.5 cm, sessile, bases acute to obtuse, margins entire, apices as basal pinnae; adaxially glabrous, abaxially sparsely covered with filiform, light brown microscales; frond texture leathery; venation distinct abaxially, slightly distinct adaxially; lateral veins nearly reaching pinna margin, pinnate, lateral veins simple. Sori small, often on distal part of pinnae, lower pinnae often not seen sori, terminal on lateral veinlets, 0.75–0.95 mm in diam., close to pinna margin, 0–10 on acroscopic side and 0–4 on basiscopic side, centers ca. 1 mm apart from one another; indusia thick, brown, small, repand, often evanescent.

Etymology: —From the Latin prefix, pseudo, false, and dangii , referring to the similarities between the new species and Polystichum dangii .

Distribution:— This species is currently found only in Ha Giang Province, northern Vietnam. It is locally quite common in Ha Giang Province. It is not found in the neighboring Chinese side of the mountains.

Notes: — We collected Polystichum pseudodangii in 2013 for the first time and we reported it as “ P. dangii ” ( Lu et al. 2014a) based on the leathery lamina texture, entire pinnae, and adjacent distributions of the two species [northern Vietnam and southern China (Guangxi and northern Guizhou); Zhang & Barrington 2013]. There are only a few species in P. sect. Haplopolystichum Tagawa (1940: 122) with leathery lamina and entire pinnae. However, our unpublished subsequent molecular work shows that the two are not even closely related.

Additional materials examined (paratypes): — VIETNAM. Ha Giang Province: Quan Ba District, Bat Dai Son Commune, Sa Phin Village , Bat Dai Son Nature Reverse , limestone mountain, 05 June 2021, N. T . Lu 07-HG2021 ( VNMN!); Nghia Thuan Commune, Bat Dai Son Nature Reserve , 23°07’57’’ N, 104°55’44’’ E, elev. ca. 1250 m, in limestone crevices, 10 December 2013, Li Bing Zhang, Liang Zhang & Ngan T . Lu 6877 ( CDBI!, MO!, VNMN!) .

Figures

FIGURE 1. Polystichum pseudodangii Li Bing Zhang, N.T.Lu & Liang Zhang.—A. Habit.—B & C. Abaxial views of portions of lamina.—D. Portion of petiole showing scales.—E. Portion of lamina showing pinnae and auricles.—F. Abaxial view of frond.—G. Adaxial view of frond.—H, J & K. Scales from petiole base, distal petiole, and rachis, respectively.—L. Indusium.