Asia-Tropical, Peninsular Thailand present, Solomon Islands present
Peninsular Thailand; throughout Malesia; Solomon Islands.
There is considerable variation in the development of indusia and in the abundance of ± elongate sori. Indusia are best developed on specimens from Perak in the Malay Peninsula. Some specimens from Sarawak and Celebes have buds at the bases of pinnae in addition to those on the costa of the apical lamina. Buds may be proliferous on plants in very humid positions (e. g. spray of waterfalls). One plant from 'alluvial forest' in the G. Mulu National Park, Sarawak, has pinnae with very broad bases, subcordate on the basiscopic side. Under T. trifolia, Copeland (l. c. 1960) appears to have included specimens of T. polymorpha.