Functional dioecy in Nothapodytes nimmoniana, a distylous species in the Western Ghats

Abstract

Nothapodytes nimmoniana (Icacinaceae) is a subcanopy tree species, commercially exploited for its wood chips that yield an anti-tumour alkaloid. The species displays intriguing sexual variation. Apart from the flowers which are comparable to typical thrum and pin morphs of distylous species, some flowers show intermediate features. We studied functional gender of the different flower types to assess the sexuality of individual plants in two populations in the Biligiri Rangan Hills Wildlife Sanctuary, Western Ghats, India. The species shows functional/cryptic dioecy. Thrum flowers are functionally males, pin flowers are females and intermediate flowers are bisexual with functional pollen and stigma. Apart from male and female plants, a small proportion of plants which are essentially males produces a small number of female and bisexual flowers. We refer to the sexual system in Nothapodytes as subdioecy and it appears to be a transitory stage in the evolution of dioecy from heterostyly.