Aims In stylar polymorphous species, the morph ratios are maintained by negative frequency-dependent selection through disassortative mating. The spatial context of a population is of crucial importance to maintain this stylar polymorphism. Under particular circumstances, disassortative mating in such species may promote the evolution of a dimorphism by gender specialization. We asked whether flexistyly can promote sufficient disassortative mating, whether the female fitness of focal plant is affected by negative frequency-dependent selection at local level, and whether the two morphs in flexistylous plants differ in gender specialization.

Methods We used open-pollinated flexistylous Alpinia mutica to compare fertility in anaflexistylous, cataflexistylous and dimorphic arrays. Second, we used neighborhood models to investigate spatial distribution of morphs at local level within the population on reproductive output in the flexistylous, A. blepharaocalyx. We quantified the distribution of the morphs in terms of neighborhood morph bias. We then measured the effect of neighborhood morph bias on open-pollinated reproductive output. Third, the reproductive characters were examined in anaflexistylous and cataflexistylous morphs of A. blepharaocalyx. We assessed functional genders of two morphs based on their allocations associated with times-dependent mating opportunities and the mean number of seeds produced by anaflexistylous and cataflexistylous plants with morph frequency in the population.

Important findings Dimorphic arrays have higher female fertility than monomorphic arrays, demonstrating the flexistyly promotes inter-morph pollen transfer. Results from A. blepharaocalyx indicate that at the neighborhood scale, the two morphs have an aggregate distribution due to clonal growth. At this scale, focal plants showed no evidence of frequency-dependent total fruits and seeds per plant or seeds per flower. These results do not support frequency-dependent selection as a major mechanism affecting morph frequencies in A. blepharaocalyx within the context of this study. There are no significant differences between two morphs in flower and fruit characters. Functional gender analyses indicate that when illegitimate fertilization is negligible, the morphs are specialized in their later sexual functions, mediated by anaflexistylous morph through male fitness gained; however, when self- fertilization is included, the two morphs are both specialized in their female functions due to the lack of inbreeding depression in the formulas.