Taxonomic Revision of the Polypodiaceous Genera of India-VI. Lepisorus excavatus Group

Abstract

In an earlier paper Bir and Trikha (1972) treated 13 species of the Polypodium lineare complex in the Himalayas, one of which was Lepisorus excavatus (Bory) Ching. Further examination of herbarium material obtained from the Central National Herbarium, Howrah, India, and the U. S. National Herbarium, Washington, has shown that there are a few more species in the Himalayas belonging to the L. excavatus complex. Taxonomically, Lepisorus (J. Smith) Ching is a most confusing and difficult genus because of the great similarity of its species and their variation (hybridization occurs between some of the species, especially those of the L. excavatus and L. kashyapii complexes). The systematic position of Lepisorus is itself controversial. It has been recognized as a distinct genus (Christensen, 1938, p. 547; Ching, 1940, p. 258; Nayar, 1961; Holttum, 1968, p. 151; Bir & Trikha, 1968a, 1972) or merged with Pleopeltis (Copeland, 1947, p. 183; Panigrahi & Patnaik, 1965). Furthermore, Lepisorus (and also Pleopeltis) have similarities with Microsorium (Bir & Trikha, 1968b). Some species of the genus also have a superficial resemblance to Phymatodes because of the similar fronds and soral arrangement, but Phymatodes can be distinguished by its hair-like, club-shaped, elongate paraphyses and by the prominent lateral veins of its laminae. Holttum (1968, p. 151) separated Lepisorus from other polypodiaceous genera and mentioned the characteristic umbrella-shaped paraphyses which protect the sporangia, especially in young stages. Although the under surface of the laminae of some of the taxa described here is covered with scales, these scales are different from those of Pleopeltis, like P. macrocarpa (Bory ex Willd.) Kaulf. In Lepisorus the laminar scales are absent or deciduous, but in Pleopeltis they are persistent. Furthermore, the rhizome scales in Lepisorus are attached towards the base, but in Pleopeltis they are centrally attached. The distinction between these two genera does not appear to be very sharp. But for the very close resemblance in external morphology and scale structure of the scaly Lepisorus species (e. g., L. oligolepidus, L. suboligolepidus, L. excavatus var. himalayensis and var. mortonianus, and L. amaurolepidus var. longifolius) with the non-scaly ones, the scaly species could have easily been included in Pleopeltis. As a consequence of our cytotaxonomic studies on the Himalayan members of Lepisorus, we discovered several new taxa. All the species treated resemble each other very closely and are sympatric. The chief diagnostic characters are in the rhizome scales and spores. The total number of fully described and illustrated