Asplenium alatulum Ching, Acta Phytotax. Sin. 9(4): 359. 1964.

Xu, Ke-Wang, Wang, Lu-Lu & Zhang, Li-Bing, 2021, Taxonomic revision of the Asplenium wrightii complex (Aspleniaceae) with reinstatement of A. alatulum and A. subcrenatum, PhytoKeys 172, pp. 75-91 : 75

Asplenium alatulum Ching, Acta Phytotax. Sin. 9(4): 359. 1964.

Type.

China. Hainan: Five-Finger Mountain, 19 May 1922, F.A.McClure 9713 (holotype: PE (PE00059412 [image!])). Fig. 3A .

Description.

Plants up to 50 cm tall. Rhizomes erect to decumbent, densely scaly; scales dark brown, narrowly lanceolate or lanceolate-ovate, 5-9 × 0.4-0.8 mm, denticulate glandular margin or long fibrillose (Fig. 2C, F, I ). Fronds tufted; stipe dull to semi-shiny, greyish-green to brown or stramineous-green, 12-25 cm, sparsely scaly, scales similar to those on rhizome; lamina triangular-ovate to elliptic, (15-)18-25(-30) × (10-)12-18(-22) cm, base truncate, apex acute, 1-pinnate (Fig. 4A ); pinnae 10-15 pairs, basal pinnae subopposite, others alternate, at an angle of ca. 60°-70° to rachis, with stalks (1-)2-4 mm, lower pinnae not reduced, suprabasal pinnae falcate-lanceolate, (5-)6-10(-12) × (0.8-)1.2-1.8(-2.0) cm, base asymmetrical, acroscopic side truncate at an angle of (55°-)65°-75(-85°) to costa, basiscopic side cuneate, becoming decurrent on rachis in apical part of lamina, margin serrate to dentate, apex acuminate (Fig. 4B, C, D ). Veins (1 or) 2-forked, with terminal hydathode. Fronds papery, brownish-green when dry, subglabrous; rachis brown to greyish-green or stramineous-green, subglabrous, terete abaxially, with greyish-green lateral wings (Fig. 4E ). Sori linear, (2-)5-9(-12) mm, on acroscopic veinlets, medial to supramedial (Fig. 4C ); indusia greyish-brown to dark brown, linear, papery, margin entire, opening towards costa, persistent. Spores with average exospore length 40-45 μm, perispore cristato-alate (Fig. 1G ).

Distribution and habitat.

Asplenium alatulum is apparently restricted to China. It grows on rocks in ravines of broad-leaved forests at an elevation of ca. 500-1600 m. (Fig. 4A ).

Additional specimens examined.

China. Hainan: Wuzhishan, Shuiman Village, elev. 870 m, 18°54'10.6"N, 109°41'15.6"E, 7 Apr 2016, K.W.Xu 107 (SYS!); the same locality, elev. 1550 m, 20 Dec 2010, X.P.Wei & R.Wei WXP113 (PE-2286681!).

Note.

Though Asplenium alatulum was thought to be an endemic species to the Hainan Island before its synonymisation with A. wrightii by Lin and Viane (2013), the morphological distinction between A. alatulum and its closely-related species was obscure due to the insufficient field investigations. In the protologue, Ching and Wang (1964) emphasised its small size, the short pinnae, the crenate-serrate pinna margins and whole rachis with lateral wings and stated that A. alatulum is markedly different from A. wrightii . However, Lin and Viane (2013) recognised that the plant and pinna size and margin shape are variable in the A. wrightii complex and included A. alatulum in the synonymy of A. wrightii . Recently, our study, based on specimen examination and recent field observations of the two species, supports their distinction.

Asplenium alatulum is distinct from A. wrightii in having erect to decumbent rhizome (vs. erect rhizome), oblong cells of scales (Fig. 2C, F, I ) (vs. quadrangle cells of scales, Fig. 2A, D, G ), winged rachis (vs. winged towards apex) and fewer pinna pairs. Phylogenetically, our earlier molecular work resolved A. alatulum in a distinct clade, sister to the clade containing A. wrightii and A. x shikokianum ( Xu et al. 2020). One accession from the Taiwan Island was nested within A. alatulum , indicating that this species should also be distributed in Taiwan.

Figures

Figure 1. Scanning electron micrographs of spore and stomata of A. alatulum, A. subcrenatum and A. wrightii A-F A. wrightii G-I A. subcrenatum J-L A. alatulum.

Figure 2. Scales of A. alatulum, A. subcrenatum and A. wrightii. A, D, G A. wrightii B, E, H A. subcrenatum C, F, I A. alatulum.

Figure 3. Type of Asplenium alatulum Ching (A barcode PE 00059412), A. subcrenatum Ching ex S. H. Wu (B barcode PE 00059494), A. wrightii Eaton ex Hooker (C barcode NY 00128031) and isotype of A. wrightii GH (D barcode GH 00020612).

Figure 4. Asplenium alatulum A Habitat and habit B Portion of lamina showing adaxial view of pinna C Portion of lamina showing abaxial view of pinna D Adaxial view of upper portion of lamina E Lower portion of rachis showing wide lateral wings.