Distylous traits in Cordia dodecandra and Cordia sebestena (Boraginaceae) from the Yucatan Peninsula

Abstract

Distyly is a genetically-controlled polymorphism with two floral morphs exhibiting spatial, reciprocal separation between stigmas and anthers; one morph has long styles and short stamens and the other short styles and long stamens. Distyly is linked to a self-incompatibility system that prevents self-pollination and crosses between plants of the same morph, thereby ensuring symmetrical mating and equal morph ratios within populations. This is the first report of distylous traits in the tropical trees species Cordia dodecandra and C. sebestena on the Yucatan Peninsula. Principal components analysis of flower morphological traits identified segregation into two groups with characteristically distylous morphology. Estimation of reciprocal herkogamy using indices showed almost perfect reciprocity in the distance between long and short sexual organs in the two flower morphs of both species. Reciprocity between organs was less exact in C. dodecandra , suggesting less accuracy in pollen transference between morphs. Self-incompatibility was observed for C. dodecandra , but could not be confirmed for C. sebestena . However, a 1:1 floral morph ratio within the sampled C. sebestena populations suggests the existence of a distylous, self-incompatibility system in this species. Morph distribution in C. dodecandra did not follow a typically distylous distribution, suggesting a disruption in population processes such as seed dispersion and seedling establishment in this species. The reported data confirm the existence of the distyly syndrome in the two Cordia species.