Polystichum unicum Li Bing Zhang, N. T. Lu & Liang Zhang 2023, sp. nov.

Polystichum unicum Li Bing Zhang, N.T.Lu & Liang Zhang, sp. nov. (Fig. 2). Type:— VIETNAM. Ha Giang Province: Vi Xuyen District, Tung Ba Commune, Du Gia National Park (Khau Ca Nature Reserve), Hom Mountain, 22°50’40’’N, 105°07’47’’E, elev. ca. 1150 m, at the top of a limestone mountain, 13 December 2013, Li Bing Zhang, Liang Zhang & Ngan T . Lu 6933 (holotype VNMN!; isotypes CDBI!, MO!) Diagnosis:— This is a very distinct species and does not seem to be similar to any species known so far in having the combination of crenulate pinna margins, distal basiscopic pinna margins forming a ca. 140° angle with the rachis, acute pinna apex, and auricles overlapping the rachis. Plants medium-sized, evergreen, 23–27 cm tall. Rhizomes erect, ca. 1 cm in diam., scales similar to those of the stipe base, but softer, crushed; roots blackish when dried, up to 12 cm long, ca. 0.3 mm in diam., densely covered with red iridescent hairs. Fronds in clusters but few, 5 or more per rhizome; stipe brown, 7–9 cm long, ca. 0.6 mm in diam., scales subulate, lanceolate or ovate-lanceolate, 0.5–3.0 × 0.4–0.8 mm, brown-blackish on abaxial side, glossy-blackish on adaxial side, thick papery, margins entire, often light brown, apex acuminate or long twisted; distal petiole scales long subulate, narrow lanceolate, 0.3–0.5 × 1.2–3.2 mm, thick membranous, margins subentire to irregular dentate, apex long-acuminate. Laminae 1-pinnate, lanceolate, 2.7–3.7 × 15–20 cm, apex long acuminate; rachises ca. 1 mm in diam., stramineous, adaxially sulcate, sparsely scaly, abaxially densely scaly; scales appressed, brown, subulate with rounded base, thick membranous, long acuminate, up to 2 mm long, margins dentate at base, irregular sparsely dentate at distal part. Pinnae ca. 22 pairs, alternate, distal basiscopic margins forming a ca. 140° angle with rachis, proximal margins attached at 75° (–90°) angles to rachis, separate, 0.6–1.1 cm distant (from attached point), acroscopic auriculate; basal pinnae obliquely oblong, 0.5–1.2 × 2.0–6.0 mm, short ...