Andromonoecious sex expression of flowers and pollinia delivery by insects in a Japanese milkweed <i>Metaplexis japonica</i> (Asclepiadaceae), with special reference to its floral morphology

Abstract

Abstract Pollination ecological studies of Metaplexis japonica Makino were carried out in central Japan. We found that the flowers were andromonoecious; the proportion of hermaphrodite flowers was 61%. Unlike other Asclepiadaceae flowers, M. japonica has a unique and outstanding long protrusion on the pistil end, which looks like a stigma. However, we confirmed that the true stigma is present on the lateral surface of the style, as it is in other Asclepiadaceae flowers. Various insects visited the flowers for nectar and the most effective pollinators were scoliid wasps. The pollen/ovule ratio was 21 and the fruit set of the hermaphrodite flowers was 11%.