Abstract
Restriction-site variation in chloroplast DNA was examined in the morphologically distinct and monotypic genus Heterogaura and the related speciose genus Clarkia (Onagraceae), both native to California. Of the 605 restriction sites surveyed, a total of 119 mutations were identified. Of these, 55 were shared by at least two species and were used to construct a most parsimonious phylogenetic tree. This analysis, as well as one based on a distance metric, provided evidence that Heterogaura and Clarkia dudleyana, a member of a phylogenetically advanced section, share a more recent common ancestor than either does with any other species. The two species are more closely related than nearly all paris of Clarkia tested. The origin of Heterogaura from within another genus raises important questions about the adequacy of morphological data and suggests that the relationships of other well-known monotypic plant genera should be reinvestigated.