18. Antrophyum Kaulfuss, Enum. Filic. 197, 282. 1824.
车前蕨属 che qian jue shu
Authors: Zhang Xianchun & Michael G. Gilbert
Plants epiphytic or epilithic, small to medium-sized. Rhizome short erect or creeping, densely covered with clathrate, iridescent scales, and roots with numerous water-absorbing root hairs. Fronds simple; lamina fleshy, or leathery, shrunken when dry, broadly lanceolate or oblanceolate, sometimes linear, spatulate, obovate, or suborbicular, rarely forked at apex, mostly gradually narrowed into a stipelike base; costa usually only present in basal part; lateral veins abundantly reticulate, without free included veinlets. Sori forming coenosorus, soral lines superficial or immersed, on lateral veins, netted or branched, less often simple; paraphyses abundant, club-shaped with a capitate head, or taeniform, or filiform. Spores trilete, tetrahedral-globose, surface low-papillate, often with scattered spherules and rodlets.
About 40 ill-defined species: Old World tropics; nine species (one endemic) in China.
The species, which badly need taxonomic revision, are either epiphytic or epilithic. In dry periods the fronds shrivel and curl up to some extent. Like most tropical plants, the species of Antrophyum reach their northernmost limits of distribution in mainland Asia, south of the Chang Jiang in C China, while along the Pacific islands up to C Japan.
Ching (Sunyatsenia 5: 201-268. 1940; Acta Phytotax. Sin. 16(3): 11. 1978) treats this genus in a rather strict sense, which does not include the tropical American Anetium Splitgerber, Polytaenium Desvaux, and Scoliosorus T. Moore. This is also supported by molecular studies (Crane et al., Amer. Fern J. 85: 283-305. 1995; Crane, Syst. Bot. 22: 509-517. 1997). Kramer (in Kubitzki, Fam. Gen. Vasc. Pl. 1: 375. 1990) believed that "Although the genus has been divided into the Old World Antrophyum s.s., with the costa evanescing above the base and paraphyses present among the sporangia, and the New World genus Polytaenium, with percurrent costa (extending to apex) and without paraphyses, the overall characters are basically not much different, yet another monotypic American genus, namely Anetium might be included in it."
The Asian species could be divided into three main groups according to the types of paraphyses, i.e., Antrophyum obovatum group with capitate paraphyses; A. henryi group with taeniform paraphyses; and A. callifolium group with filamentous paraphyses. Antrophyum obovatum group might be the most primitive group, while A. callifolium group might be the most advanced one in this genus.
Knapp (Ferns Fern Allies Taiwan, 422, 434. 2011) recorded Antrophyum alatum Brackenridge, described from the Pacific islands, from Taiwan but noted that further studies are required to determine if this species is conspecific with A. callifolium.