A natural hybrid (2n = 21) between the parapatric rain forest species Monophyllaea hirtella (2n = 20) and M. horsfieldii (2n = 22) (Gesneriaceae) has been observed at Sg. Lubuk Paraku, Padang, W. Sumatra. The hybrids showed intermediary characters between the parental species in the inflorescence structure, flower size and colour, indumentum, chromosome numbers, and habitat. The 29% pollen fertility of a single hybrid specimen suggests that the genetical isolation between the parental species may break down and reproduction over subsequent generations may occur. © 1990 Springer-Verlag.
