A Redefinition of the Genus Hemionitis

Abstract

In the summer of 1971 during field work on the ferns of the state of Oaxaca, Mexico, I collected four species of the genus Hemionitis, only one of which had previously been reported from that state. A broader examination of the genus was undertaken in order to determine the species' limits and relationships. Spore studies showed that certain species of Hemionitis had spores that closely resembled those of some species of the closely allied Gymnopteris, and so the study was broadened to include the species of both genera. Hemionitis L. (1753) is typified by H. palmata (Underwood, 1899, p. 254) (Fig. 12), a species which ranges from Mexico to northern South America and the West Indies. Linnaeus included in Hemionitis ferns with so-called gymnogrammoid sori (those which run along the veins and lack an indusium). Many ferns with this type of sorus were placed in the genus Gymnogramma by Desvaux (1811, p. 304) and more extensively by Hooker and Baker (1868), but gradually species were removed in blocks to such genera as Pityrogramma, Eriosorus, Bommeria, Anogramma, and Gymnopteris. The genus Hemionitis as commonly construed today includes the widespread H. palmata, H. pinnatifida (southern Mexico to Costa Rica; Fig. 6), H. levyi (southern Mexico to Costa Rica; Fig. 7), H. elegans (southwestern Mexico; Fig. 5), H. smithii (Jamaica; Fig. 10), and H. arifolia (southeastern Asia; Fig. 6). The disjunct H. arifolia was cause for some concern, and closer examination showed that it also was quite different from the New World species in the scales on the blade, the dark color of the leaf tissue, the more coriaceous texture, the sagittate leaf architecture, the buds at the base of the blade rather than on the margin, and the spores, which have noticeably high ridges, as opposed to the tuberculate spores of H. palmata. Thus, there was some justification for establishing a new genus based on H. arifolia, but subsequent inclusion of the genus Gymnopteris in the study made this hypothesis untenable. Gymnopteris Bernhardi (1799, p. 297) is based onAcrostichum rufum (L.) L. (= G. rufa (L.) Bernhardi). In the present study five species of Gymnopteris were examined: G. rufa (West Indies, Central and northern South America; Fig. 9), G. tomentosa (South America; Fig. 8), G. subcordata (Mexico to Nicaragua; Fig. 3), G. vestita (southeastern Asia; Fig. 2), and G. bipinnata (southeastern Asia; Fig. 1). Gymnopteris is said to differ from Hemionitis on the basis of its pinnate architecture and free veins. Other than the pinnate architecture, there are no characters which consistently distinguish the two genera. Other characters contradict the separation of these two genera, and I find a stronger argument for combining the two genera.