Taxonomic studies of lycophytes and ferns from the Pan-Himalaya (I): Hymenophyllum (Hymenophyllaceae)

Abstract

The present account deals with the filmy fern of genus Hymenophyllum from the Pan-Himalaya, as a precursor of the ongoing "Flora of Pan-Himalaya" project, which aims to update the taxonomy of the vascular plants from the Himalayas and adjacent mountainous regions. More than one hundred specimens of Hymenophyllum especially that grown in the Pan-Himalaya deposited in the China National Herbarium (PE) have been carefully examined, in comparison with the collections from the Himalayas kept in European herbaria (K, BM, and E). The morphology and anatomy of each specimen were studied and photographed. As a result, ten species were recognized and described in detail, key to species, photography illustrations of plant habit, leaf shape and margin, lamina cells and veinlets, and sori are provided to facilitate correct identification of plants. According to the most recent classification system of the filmy ferns, the genus Mecodium is no longer accepted, although the leaf margins of Mecodium are all entire. Hymenophyllum barbatum, H. denticulatum, H. exsertum, H. levingei, and H. simosianum belong to subgenus Hymenophyllum; H. corrugatum, H. longissimum, H. polyanthos belong to subgenus Mecodium; H. badium and H. javanicum belong to subgenus Globosa. It is noticed that Hymenophyllum species often distribute in forests of middle to high altitudes from 2000-3000(4000) m in the Himalayas. Among these, Hymenophyllum corrugatum and H. longissimum are endemic species to China, while H. levingei is globally threatened.