Patterns of mating system evolution in Cryptantha section Oreocarya (Boraginaceae): A phylogenetic approach

Molecular phylogenetic methods provide new and powerful ways to test hypotheses concerning the evolution of breeding systems. These methods allow one to infer the number of evolutionary transitions for specific reproductive characters, thereby providing a framework for existing models of breeding system evolution to be tested using exemplar systems. Character mapping has provided insight into the evolution of plant breeding systems by suggesting the number and direction of changes in many key reproductive characters, including those that define specific syndromes, e.g., dioecy, androdioecy, self-incompatibility and heterostyly (Weller and Sakai, 1999).; Heterostyly involves the reciprocal placement of anthers and stigmas among two (distyly) or three (tristyly) flower morphs, and is usually accompanied by a sporophytically controlled diallelic incompatibility mechanism that prevents self- and section Oreocarya of the genus Cryptantha (Boraginaceae) contains species that exhibit breeding system characters intermediate to those classically found in heterostylous systems. The goal of this study was to determine the order of events that lead to heterostyly for Cryptantha thereby testing the current models for the evolution of this syndrome. Measurements of the stigma position, anther position, and corolla length indicate that stigma height and anther height do not always change between pins and thrums of the same species. Additionally, the size of the corolla is related to the degree of spatial separation between the floral organs. All of the dimorphic species are at least partially self-compatible, while some monomorphic species exhibit incompatibility. Genetic variation among the Oreocarya is limited, and plant species distribution for the section is correlated with geology. The phylogenetic analyses indicated that the heterostylous state may be ancestral in Oreocarya, and it appears that the breeding system is in the process of breaking down, making it difficult to test the models for the evolution of the syndrome.