The Systematics Of Lithospermum L. (Boraginaceae) And The Evolution Of Heterostyly

Abstract

Lithospermum L. (Boraginaceae) includes ca. 60 species. The genus has a nearly cosmopolitan distribution, being native to all continents except Australia and Antarctica. The center of diversity for the genus is Mexico and the southwestern United States, and approximately three-quarters of the species of Lithospermum are endemic to this region. Lithospermum and the tribe to which it is assigned, Lithospermeae, have been the subject of recent phylogenetic analyses, but these analyses have been limited in their scope. In order to examine critically the phylogenetics of Lithospermum and its relatives, three matrices, each consisting of 67 taxa, were constructed. The molecular matrix includes 10 chloroplast DNA regions, and the morphological matrix is composed of scores for 22 morphological characters. The combined matrix comprises the data from both of these matrices. Analyses of these matrices resolve Lithospermum as non-monophyletic, because members of other New World genera of Lithospermeae are found to be nested among species of Lithospermum. Because Lithospermum, as traditionally circumscribed, was resolved as non-monophyletic, the circumscription of the genus is expanded to include all species of New World Lithospermeae. Additionally, the phylogenetic distribution of various molecular and morphological characters was examined. One character, heterostyly, arose multiple times among the species of Lithospermum. The floral developmental patterns of three heterostylous and three homostylous species of Lithospermum were investigated. Although heterostyly may have originated independently in each of these three species, the floral developmental patterns of the long-style and short-style morphs of heterostylous species of Lithospermum are similar to those of homostylous relatives with approach and reverse herkogamous flowers, respectively. Despite similar gross floral developmental patterns, the developmental patterns of the stylar epidermal cells differ among the heterostylous species. In addition to phylogenetic and floral developmental studies, a revision of the species of Lithospermum of Mexico was undertaken, and species boundaries were reevaluated. Three new species are described from northern Mexico - L. chihuahuanum, L. kelloggiae, and L. tenerum - and each is known only from its type specimen. 2