Arachniodes vietnamensis Liang Zhang, N.T.Lu & T.T.Nguyen, 2021

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 : 260-261

Arachniodes vietnamensis Liang Zhang, N.T.Lu & T.T.Nguyen , sp. nov., Fig. 2 .

Type: — VIETNAM. Lam Dong Province: Bidoup-Nuiba National park, by stream near K'long Lanh Station , elev. 1600 m, Li-Bing Zhang et al. 8602 (holotype PHH!, isotypes CDBI!, MO) .

Diagnosis: — The new species is most similar to Arachniodes chinensis in having dense, black, appressed, and subulate scales on rachis, laminae more or less ovate, apices gradually acuminate, and lateral pinnae lanceolate. Compared to A. chinensis , the new species has laminae shortly ovate (vs. ovate-deltoid), 5 to 7 pairs of pinnae (vs. often 2–4 pairs in the later), pinnules lanceolate to narrowly oblong with deep lobes (vs. pinnules broadly oblong, slightly lobed or unlobed in the later), often two pairs of basiscopic pinnules of basal most pinnae elongated (vs. one pair in the latter).

Plant 56–65 cm high. Rhizome short-creeping. Stipe in similar length as lamina, ca. 29 cm, 2.5 mm in diam., densely scaly, scales blackish brown, linear-lanceolate or subulate 8.5–11 × 1.3–1.5 mm, slightly dentate or denticulate, upwards with appressed filiform scales. Lamina 2-pinnate or 3-pinnate, dark brown or dull green when dried, shortly ovate, 25–29 × 14–21 cm, papery, base cordate, apex caudate, up to 17 cm long, rachis scales as those on distal portion of stipe. Pinnae 5–7 pairs, 0.7–3.5 cm apart, deltoid-lanceolate or lanceolate, 4.5–14.5 × 1.3–5.5 cm, alternate, or lower 1(or 2) pairs sometimes opposite, shortly stalked, to 0.4 cm, those of upper pinnae subsessile; basal most pinnae deltoid-lanceolate, 12–14.5 × 4–5.5 cm, two basiscopic pinnules elongated to 3.5 cm, base acute; pinnules ca. 18 pairs, shortly stalked to 0.1 cm, or sessile, lanceolate or narrowly oblong, 0.5–1.8 × 0.3–0.6 cm, gradually shortened, base cuneate, apex acute or obtuse, deeply lobed, margin aristate; axes and veins of ultimate segments with brown microscales abaxially. Sori terminal on veinlets, 0.8–1.2 mm, 1 – 7 pairs per ultimate segment, medial between midveins and margins; indusia 0.6–1.0 mm in diam., dark brown, firmly membranous to thick, subentire to sparsely ciliate; spores ellipsoid, 28.6–47 µm in diam., compressed folds, sparsely echinulate, perforate.

Etymology:— The specific epithet, vietnamensis , is derived from the name of the country where the new species was discovered, Vietnam.

Geographical distribution:— So far, the new species has been found in four provinces of Vietnam, including Quang Binh Province, Quang Tri Province and Thanh Hoa Province in central Vietnam, and Lam Dong Province in the Central Highlands .

Additional material examined:— VIETNAM. Quang Binh Province: Bo Trach district, Phong Nha-Ke Bang National Park , scattered on rather wet places in slightly logged broad-leaved forest, elev. ca. 650 m, 17°27'30"N, 106°23'06"E, 7 December 2004, Wu S. K . et al. wp-904 ( KUN!); Bo Trach district , in slightly logged broad-leaved forest, elev. ca. 800-900 m, 17°28'36"N, 106°22'39"E, 11 December 2004, Wu S. K . et al. wp-1065 (KUN!); Quang Tri Province: Huong Hoa District, Bac Huong Hoa Nature Reserve, Huong Phung Commune, Chênh Vênh villige, along Sa Mù stream, elev. 1300 m, 16°48'12.06"N, 106°35'55.52"E, 19 November 2014, Zhang L. B . et al. 7575 (VNMN!, CDBI!); Thanh Hoa Province: Pu Luong Nature Reserve, Mt. Pu Luong , elev. 1200 m, 20°28′44.06”N, 105°05′28.29”E, 16 October 2014, Zhang L. B . et al. 7111 (VNMN!, CDBI!, MO!); Lam Dong Province: Bidoup- Nuiba National Park, by stream near Hon Giao Station , elev. 1750-1800 m, 18 October 2015, Zhang L. B . et al. 8493 (PHH, CDBI!).

Notes:— Similar to Arachniodes libingii , A. vietnamensis could easily be identified as A. chinensis . However, in addition to their relative distant phylogenetic relationships ( Lu et al. 2019a), A. vietnamensis differs from A. chinensis in having more pairs of pinnae, lanceolate to narrowly oblong pinnules, and lobed pinnules of lower pinnae ( Fig. 3 ).

Generally, Arachniodes chinensis , A. libingii and A. vietnamensis are different from each other in lamina shape, number of pinnae, and the shape of lamina apices ( Fig. 3 ), and can be distinguished following the below dichotomous key:

1. Laminae deltoid-oblong, apices abruptly acuminate-caudate, pinnae 6 to 8 pairs............................................................. A. libingii

-. Laminae ovate or ovate-deltoid, apices gradually acuminate, pinnae 2 to 7 pairs.............................................................................2

2. Laminae deltoid-ovate, pinnae 2 to 4 pairs, basal most pinnae often with one pair of pinnules elongate, pinnules broad oblong, shallowly lobed................................................................................................................................................................ A. chinensis

-. Laminae ovate, pinnae 5 to 7 pairs, basal most pinnae often with two pairs of pinnules elongated, pinnules lanceolate to narrowly oblong, deeply lobed .................................................................................................................................................. A. vietnamensis

Figures

FIGURE 2. Arachniodes vietnamensis Liang Zhang, N.T. Lu & T.T. Nguyen,—A. Abaxial surface of frond.—B. Portion of upper lamina.—C. Abaxial surface of pinnules.—D. Lateral pinnae.—E. Sori and portion of rachis showing densely appressed subulate/filiform scales.—F. Scales on stipe.—G. Scale on rachis.—H. Sparse, echinulate, perforate spore.—I. Perispore.—J. Indusia. Photo credit: Xinmao Zhou & Ngan Thi Lu.

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).