Arachniodes libingii Liang Zhang, N.T.Lu

Lu, Ngan Thi, Nguyen, Linh Phuong, Le, Chi Toan, Nguyen, Thanh Trung & Zhang, Liang, 2021, Arachniodes libingii sp. nov. and A. vietnamensis sp. nov. (Dryopteridaceae), two new ferns from southern China and central Vietnam, Phytotaxa 522 (3), pp. 256-262 : 257-259

Arachniodes libingii Liang Zhang, N.T.Lu & T.T.Thanh, sp. nov., Fig. 1 .

Type: — CHINA. Hainan Province: Wuzhishan , elev. 1050 m, 18°54′5.69”N, 109°41′23.87”E, in broad-leaved evergreen forests, 14 December 2012, Liang Zhang 1621 (holotype CDBI!, isotype CDBI!) .

Diagnosis: This species is most similar to Arachniodes chinensis ( Fig. 3 : A, D) in having short creeping rhizomes, scales on basal stipes blackish brown, scales on fronds dense, black, appressed, and subulate, laminae 2-pinnate, and indusia entire, but the former has deltoid-oblong laminae and longer (up to 18 cm) caudate apices (vs. deltoid-ovate laminae and shorter caudate apices in the latter), and up to 8 pairs of pinnae (vs. often 2–4 pairs in the latter).

Plant 57–67 cm high. Roots 7–9, 1– 9 cm × 0.2–0.5 mm. Rhizome short-creeping, 6.0 × 0.9 cm; densely scaly, brown when young, dark brown when mature, narrow filiform-lanceolate, 4–7 × 0.2–0.5 mm, entire. Stipes stramineous to brown, 27–30 cm × 2.5 mm; base densely scaly, dark brown, subulate, lanceolate, 4–11 × 0.1–0.9 mm, entire, apex shortly tortuous; upward densely scaly, scales appressed, black, subulate, 1.3–2.8 × 0.2 mm. Lamina 2- pinnatepinnatifid, dull green when dried, deltoid-oblong, papery, base acute or broad obtuse, apex abruptly acuminate to long caudate, up to 18 cm long; rachis 1.2–1.8 mm in diam., rachises and axes with dense scales abaxially and adaxially, scales appressed, subulate, similar to scales on distal stipes but smaller; pinnae 6 to 8 pairs, lowest pinnae deltoid, basal basiscopic ones slightly longer or elongated, upper pinnae lanceolate, 5.5–20 × 1.3–3.6 cm, base acute or obtuse, apex long, narrowly acuminate; pinnules 7–22 pairs, alternate, shortly stalked to sessile, oblong, 0.7–2.6 × 0.3–0.7 cm, with brown microscales abaxially, scales 0.2–0.5 mm, glabrous adaxially, base auricle, acute, apex acute or obtuse, aristate. Sori small, 0.7–1.5 mm, terminal on veinlets, 1–13 pairs per ultimate segment, medial between margins and mid-veins, fugacious; sporangia dark brown; indusia ca. 0.5 mm in diam., brown, membranous or thickly membranous, entire; spores unseen.

Etymology:— The specific epithet, libingii , is in honor of Dr. Li-Bing Zhang, a botanist based at Missouri Botanical Garden, USA, for his great contributions to pteridology of China and worldwide. He was also one of the thesis advisors of both N.T.L. and L.Z.

Geographical distribution:— The new species currently occurs in Hainan and Guangdong, the two southernmost provinces of China. It is possible that Arachniodes libingii also occurs in other provinces of southern China.

Additional material examined:— CHINA. Guangdong Province: Lianzhou , elev. 255 m, 25°2′37.39"N, 112°25′12.65"E, 27 September 2010, Liang Zhang 1199 ( CDBI!) ; Hainan Province: Qiongzhong, Tiedingling , elev. 1100 m, 18°56′N, 109°43′E, 26 May 2002, Dong S. Y. 647 ( PE!); Wuzhishan , elev. 1400 m, 18°53′N, 109°41′E, 17 December 2004, Wuzhishan Fern Survey 116 ( PE!); Wuzhishan, elev. 960 m, 18°52′N, 109°40′E, 22 December 2004, Wuzhishan Fern Survey 243 ( PE!) .

Notes:— Arachniodes libingii could be confused with A. chinensis and A. yaoshanensis due to their morphological similarities. Comparing to the two species, A. libingii differs from A. chinensis in having more pairs of pinnae and lamina apices abruptly acuminate to long caudate ( Fig. 3 : A, B), and differs from A. yaoshanensis in having ovate-oblong laminae, rhombic-oblong pinnules, and densely black scales on rachis and petioles. Our previously phylogenetic analysis found somewhat distant relationships among the three species, with A. libingii being resolved in the Vietnamensis Group of the Arachniodes Clade, A. chinensis in the SC ( Simplicior - Chinensis ) Group of the Arachniodes Clade, and A. yaoshanensis in the Assamicae Clade ( Lu et al. 2019a). The most closely related species to A. libingii is an unknown species from Japan and Taiwan Island. They together formed a lineage resolved as sister to A. vietnamensis .

Figures

FIGURE 1. Arachniodes libingii Liang Zhang, N.T.Lu & T.T.Nguyen,—A. Habit.—B. Stipe base with darkish brown scales.—C.Young rhizome.—D. Upper pinnae with lamina apex.—E. Pinnules with young sori.—F. Pinnules with mature sori.—G. Portion of abaxial lamina with apex.—H. Portion of middle pinnae.—I. Portion of basal most pairs of pinnae. Photo credit: Liang Zhang.

FIGURE 3.—A-C. Fronds showing the differences in laminae and pinnae between three species (A. Arachniodes chinensis, B. A.libingii, C. A. vietnamensis).—D-F. Portion of laminae, showing the basal most pinnae with elongated pinnules (D. A. chinensis, E. A. libingii, F. A. vietnamensis).