The genus Gynostemma is represented in Thailand and Malesia by four species of which the extremely variable G. pentaphyllum is widespread covering the whole area. Seven forms are recognized in G. pentaphyllum, of which three are new: forma fasciculare W.J. de Wilde & Duyfjes, forma grandiflorum W.J. de Wilde & Duyfjes, forma knemandrum W.J. de Wilde & Duyfjes, and three are new combinations: forma dasycarpum (C.Y. Wu) W.J. de Wilde & Duyfjes, forma pubescens (Gagnep.) W.J. de Wilde & Duyfjes, and forma simplicifolium (Blume) W.J. de Wilde & Duyfjes. Two new species, both endemic to New Guinea, are described: G. intermedium W.J. de Wilde & Duyfjes and G. papuanum W.J. de Wilde & Duyfjes.