Floral morphs and seed production from hand-pollination in a population of Oxalis corymbosa in Taiwan

Oxalis corymbosa , a tristylous species, lacks seed-set in Taiwan. In a previous survey, six floral types (3 floral morphs in combination with two types of anthers) of 23 populations in Taiwan were assigned based on qualitative visual observation. In this study, we conducted experiments on one of the populations to pursue following objectives: to analyze the floral types of the population based on quantitative measurement and to test the hypothesis that the lack of seed-set is partially attributed to pollination limitation. The heights of anthers and stigmata were measured and analyzed. The number of viable pollen grains per anther was estimated. Pollen germination and seed-production after hand-pollination treatments were examined. Variations in anther and stigma heights were found in each type of previously assigned flowers. Unequal heights of reciprocal sexual organs between floral types were also found. Each level of anthers of MS-Y (mid-styled bearing yellow anthers) and SHS-Y (semi-homostylous bearing yellow anthers) flowers contained about 60 and 25 viable pollen grains, respectively; while anthers of SHS-W (semi-homostylous bearing white anthers) flowers had no pollen. Among hand-pollination treatments of inter-morph, cross-intra-morph and self-intra-morph crossings, only in one inter-morph crossing, i.e. SHS-Y (pollen receiver) × l/MS-Y [pollen donor, pollen from lower (l)-level anthers of MS-Y], pollen tubes were found entering micropyles of the ovules, and seeds were built. Thus, this species can produce seeds by hand-pollination. The result supports that limitation of pollen transfer at least partially contributes to the absence of seed-production in field populations of O. corymbosa in Taiwan.