Female sterility and ovule malformation of Oxalis corymbosa, an exotic plant in Taiwan

Abstract

Investigating reproductive biology is relevant in evaluating the invasive capacity of alien plants. Low quality of pollen grains of an exotic plant, Oxalis corymbosa, in Taiwan has been found in a previous study. The objectives of this study were to evaluate the female fertility and to examine the morphology and ontogeny of ovules of O. corymbosa, in Taiwan. Cleared whole-mount, resin embedded sections and paraffin sections of pistils and ovules of flowers of two different morphs of the plant were made and observed. The observation revealed that O. corymbosa has anatropous and bitegmic ovules. Most of the observed megasporangia in ovules of flowers during anthesis were developmentally arrested. A 4-celullar, 5-nucleate female gametophyte (embryo sac), containing one egg cell, two synergids, and one central cell with two polar nuclei, was rarely (about 2%) observed in ovules of fully-open flowers. Observations of flower buds of different lengths revealed that multiple abnormalities occurred in the development of megasporangia and in cells of integuments. Consequently, most of mature ovules observed contained no or develop-arrested embryo sacs (female gametophyte). The result confirmed female sterility of O. corymbosa in Taiwan. The ecological implications of the absence of sexual reproduction of the exotic plant in Taiwan is discussed.