Distyly in Psychotria serpens (Rubiaceae) in the Ryukyu Islands, Japan

概要

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Variation in several floral traits was examined to determine floral dimorphism in three populations of Psychotria serpens from Amami-Oshima and Okinawa islands, Japan. Two populations on Amami-Oshima exhibited long-styled and short-styled morphs that differed reciprocally from each other in stigma and anther heights, while a population on Okinawa was composed of long (L)-styled, short (S)-styled, and short homo (H)-styled morphs. In the L- and S-styled morphs, most flowers usually produced pollen grains stainable with aniline blue in lactophenol. Pollen grains from the S-styled morph were significantly larger than those from the L-styled morph, but no major difference was found between the two morphs in exine sculpturing. In the H-styled morphs, most flowers usually lacked pollen grains or did not produce stainable pollen grains. In some peculiar flowers, however, a few stamens that were exserted from the corolla tube rarely produced stainable pollen grains in the H-styled morph; the diameter of the pollen grains was in accordance with those of the S-styled morph. These observations suggest that P. serpens in the Ryukyu Islands is fundamentally distylous and sometimes includes short H-styled morphs within a population, the stamens of which are frequently abortive. Considering the nature of the peculiar flowers, the short H-styled morphs appear to be a consequence of unusual floral development.
2013-10-31