Thesis (M.Sc.)--Chulalongkorn University, 2004

Thelypteris Schmidel s.l. is one of the large genus of the Thelypteridaceae. It is comprised of about one thousand species, mostly occur in tropical and subtropical regions of the world. Up to now, Thelypteris s.l. cannot be clearly classified due to different generic concepts of pteridologists. Some authors, treated all species in a single genus, whilst the others segregated Thelypteris s.l. into many genera. In Thailand, Thelypteris s.l. is commonly found in various habitats throughout. Fifty one species were reported in Flora of Thailand and treated into two genera. In contrast, there were 16 genera according to Holttum's classification. In order to clarify this taxonomic inconsistency, 518 OTUs from 27 species were analysed using cluster and canonical discriminant analyses. The total of 21 quantitative and 11 qualitative characters were employed. In cluster analysis using only quantitative characters, the Thelypteris s.l. could be separated into three taxa: Thelypteris s.s., Macrothelypteris and Pronephrium at average taxonomic distance 1.50. The same result was obtained when both quantitative and qualitative characters were used. Likewise, canonical discriminant analysis suggested that there were three groups within the genus Thelypteris s.l. The three groups/genera can be distinguished on the basis of scale width, angle of basal pinnae to rachis, number of annulus cell, spore height and spore diameter. In all, the results from these morphometric analyses support the segregation of Thelypteris s.l. into three genera, viz. Thelypteris s.s., Macrothelypteris and Pronephrium.