Incompatibility and Pollination of Distylous Psychotria serpens (Rubiaceae) in the Ryukyu Islands, Japan

Psychotria serpens (Rubiaceae) is usually distylous in floral morphology, but uncertainty still remains as to whether the two morphs of the species have self- and intramorph-incompatibility system and also on the efficiency of pollinators. We examined self- and intramorph-incompatibility as well as efficiency in flower visitors to carry out pollination in natural populations. Pollination experiments indicated that P. serpens is self- and intramorph-incompatible, as in other typical distylous species. Flowers of the two morphs produced nectar from the base of the corolla tube and attracted various insects, such as short tongued wasps, bees, hoverflies, butterflies, etc. Among the flower visitors, the short-tongued wasps, bees and hoverflies were considered to be efficient pollinators for P. serpens in the Ryukyu Islands.