17. Asplenium castaneoviride Baker, Ann. Bot. (Oxford). 5: 304. 1891.
东海铁角蕨 dong hai tie jiao jue
Asplenium kobayashii Tagawa; ×Asplenosorus castaneoviridis (Baker) Nakaike.
Plants 8-20 cm tall. Rhizome erect, short, scaly; scales black, narrowly triangular. Fronds caespitose; stipe adaxially green, abaxially shiny castaneous, subglabrous; lamina pinnatisect, dimorphic and variable; stipe of small fronds 2-4 cm, of large fronds 6-8 cm, lamina of small fronds narrowly triangular to linear, 5-9 × ca. 1 cm; lamina of large fronds ovate-lanceolate, 11-14 × 2-5 cm, attenuate to both ends, apex acuminate; pinnae 7-9 (small fronds) or 10-15 pairs, opposite or subopposite, sessile, lower segments of large fronds reduced and gradually more triangular-deltoid, middle segments narrowly triangular, 1-2 × 0.3-0.5 cm, base asymmetrical and adnate to rachis, acroscopic side (sub)auriculate, basiscopic side decurrent into narrow wing along rachis, margin repand to sinuate, apex obtuse; segments of small fronds elliptic to obovate, lowest segments largest, 5-8 × 0.3-0.5 cm, adnate to rachis, margin serrate, apex obtuse. Veins anadromously pinnate, obscure, veins simple or forked ending in submarginal hydathode. Fronds herbaceous, green to yellowish green when dry; rachis green, (sub)glabrous. Sori 3-6 per pinna, linear-elliptic, ca. 2 mm, on acroscopic veinlets; indusia green, linear-elliptic, entire, opening toward costa.
On rocky cliffs. Jiangsu, Liaoning, Shandong [Japan, Korea].
We consider Asplenium castaneoviride to be a good species, not a sterile hybrid (Ching & Iwatsuki, J. Jap. Bot. 57: 129-132. 1982) because Lovis et al. (Brit. Fern Gaz. 10: 263-268. 1972) and Lin and Sleep (in K. H. Shing & K. U. Kramer, Proc. Int. Symp. Syst. Pterid. 111-127. 1989) have shown that this is a fertile allotetraploid, which originated via chromosome doubling in the sterile hybrid between A. ruprechtii and A. incisum.