Breeding system and pollination ecology of two Abrus species (Fabaceae) from tropical West Africa

The pollination and breeding strategies of two Abrus species (A. precatorius L. and A. pulchellus Wall. ex Thw.) were comparatively investigated in Nigeria, West Africa. Observations were made on the phenology, floral morphology and architecture, breeding and pollination system, as well as flower-insect interactions. During 1999–2000, Abrus precatorius was observed to flower twice a year (April to June and September to November) while A. pulchellus flowered only once, from October to December. Flowers of A. precatorius never opened, which indicted obligate cleistogamy in this species. The study has produced evidence showing that the type of breeding strategy in A. pulchellus is of the facultative type. There was no evidence of agamospermy in the two species. Fourteen insects and an arachnid belonging to eleven families in six orders were observed visiting flowers of the two species. Among these visitors, Chrysops longicornis, Riptortus dentipes, Rhinocoris bicolor and Rhinocoris rapax were the most likely to aid cross-pollination and hence are legitimate visitors. Our study suggests that low outcrossing rate occurs in both species despite the predominant cleistogamous characteristics in the genus. Occurrence of low outcrossing is a kind of evolutionary homoeostasis in both species for perpetuating healthy offspring.