Pollination ecology of Rhynchosia cana (Willd.) DC. (Fabaceae), an erect sub-shrub, in peninsular India

Abstract

Rhynchosia cana is a perennial erect sub-shrub. It flowers during November-January with peak flowering in December. The flowers are hermaphroditic, nectariferous, self-compatible and display explosive pollination mechanism adapted for pollination by bees. They do not fruit through autonomous selfing, but rather through manipulated selfing, geitonogamy and xenogamy mediated principally by bees and occasionally by lycaenid butterflies. In the localities of this herb, weeds such as Hyptis suaveolens (Lamiaceae) and Chromolaena odorata (Asteraceae) show luxuriant growth and flower simultaneously, and their intense flowering and high flower density ensures that most flower-visiting insects visit their flowers. In this situation only two bee species, Nomia and Anthidium exhibited fidelity to R. cana flowers. Un-tripped flowers fall off while tripped ones set fruit. In open-pollinations, fruit set was 81% and seed set was 54%. Seed dispersal occurs by explosive pod dehiscence. Perennial root stock resurrects back to life and restarts its reproductive cycle during the rainy season. Seeds also germinate at the same time but their continued growth is subject to the availability of soil moisture content. This study suggests that R. cana is unable to compete with the co-flowering weed species for pollinators, and also has regeneration constraints due to nutrient-deficient rocky habitats with prolific growth of weeds.

Keywords

• entomophily
• explosive pollination mechanism
• explosive seed dispersal
• hermaphroditism
• rhynchosia cana.