A Reinvestigation of the Morphology of Hypodematium crenatum

Abstract

Taxonomically as well as phylogenetically the small fern genus Hypodematium remains a problematic one. It includes the widespread, pantropic species H. crenatum (Forsk.) Kuhn and perhaps three or more other species, each of limited range in the ChinaJapan region; some pteridologists detect as many as 16 species. The genus has been associated with the woodsioid, tectarioid, athyrioid, and thelypteroid ferns by different taxonomists, and in some cases even by the same taxonomist at different times. Morphologically the genus is little known except for some aspects of H. crenatum published by Hayata (1927), Mehra and Loyal (1956), Loyal (1960), and Iwatsuki (1964a, b). Since the descriptions of these authors contain some discrepancies, we thought it worthwhile to reinvestigate the morphology of H. crenatum and to see whether the morphology of this plant could yield some additional clues as to the relationships of the genus. Material for this study was collected growing in rock crevices from Chakrata (Central Himalaya) and was then cultivated in the fernery of the National Botanic Gardens. Spore morphology was studied using standard palynological techniques, as described by Nayar and Devi (1964). Prothalli were grown on sterilized nutrient agar medium in petri dishes maintained at 24 =t 2? C and at about 600 ft-c intensity, as described by Nayar (1962). The source was fluorescent day light lamps for 12 hours in each day. Vascular organization of the rhizome was studied from steles excavated mechanically from the rhizome, as well as from reconstructions based on camera lucida drawings of serial microtome sections. THE RHIZOME is thick, creeping, cylindrical, bears several dormant branches on the ventral surface, and is densely covered by basally attached, golden brown, lanceolate, thin-walled paleae about 30 X 3 mm (Fig. 3) mixed with profuse, unicellular, papillate, glandular hairs (Fig. 7). The apex of the palea is uniseriate and 107