The floral dimorphism in the rare endemic plant, Abeliophyllum distichum Nakai (Oleaceae)

Abstract

Heterostyly is clearly confirmed in the Korean endemic, monotypic taxon Abeliophyllum distichum Nakai (Oleaceae) by studies of plants from two geographically isolated populations. Variation in the hitherto unreported floral morphological aspects including an extended study of pollen grains of A. distichum in association with distyly were studied and described in details by using stereo-microscopy, LM and SEM. In this plant styles are always significantly longer in pin flowers than in thrum flowers, and the same is also true for the size of stigma including stigmatic papillae between two morphs (P < 0.0001). Thrum flowers have significantly larger petals and longer stamens then pin flowers (P < 0.0001). Dimorphism of pollen size in relation to distyly is generally well correlated and significantly different; the thrum flowers are significantly larger than those of the pin flowers (Yul-ji-ri population: P < 0.001, Hongryung population: P < 0.0001, respectively). The thrum pollen grains have slightly larger lumina than those of the pin pollen grains, but the difference between two morphs was only marginally or not significant. The exine thickness between two morphs was not significantly differentin both studied populations. In Song-duk-ri population the two morphs do not occur in a 1:1 ratio (i.e., anisoplethy). Bees of Apis sp. and Lasioglossum sp. (both in Apidae) were found as flower visitors in A. distichum. Floral dimorphism of A. distichum with respect to heterostyly is also briefly discussed.