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.
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