Systematics, evolution, and biogeography among Dracaenoid genera: Dracaena, Pleomele, and Sansavieria (Asparagaceae)

Abstract

This study presents the molecular evolutionary relationships among the ambiguous three plant genera Dracaena Vand. ex L., Pleomele Salisb., and Sansevieria Thunb. (dracaenoids) first described in the 18th century. The taxonomy of dracaenoids has many ambiguities and until present there have been no molecular systematics study addressing this issue. This dissertation provides the first complete molecular phylogenetic study to include a thorough representative collection of dracaenoids and discusses their systematics and biogeography on a global scale. At a more local scale, population genetics of two endemic Hawaiian Pleomele species (one endangered and one common) were done for expanding our biological knowledge of these species and assessing conservation needs based on results of random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) data. The relationships of dracaenoids with combined chloroplast DNA sequences were reconstructed. The combined dataset was analyzed using parsimony, Bayesian, and maximum likelihood. The combined dataset was analyzed using parsimony, maximum likelihood, and Bayesian analysis. Results show that 1) the monophyly of dracaenoids is confirmed; 2) the Hawaiian Pleomele species are the sister group to the remainder of the dracaenoid phylogeny; 3) the species Dracaena and Pleomele are intermixed; 4) Sansevieria is monophyletic, but is nested within Dracaena; 5) the Central American species D. americana and D. cubensis are the basal group to the remainder of the dracaenoid species. The common ancestor of dracaenoids is from Asia rather than Africa where the center of diversity among dracaenoids is located. Based on these results, a new combination recognizing the Hawaiian species of Pleomele as a distinct genus, Chrysodracon, and combining the three remaining genera all into Dracaena is proposed. Chapter 3 examines the evolutionary history and biogeography of the endemic tree genus Chrysodracon (formerly the Hawaiian species of Pleomele). The results provide clear evidence of the monophyletic relationship of these species, their biogeographical patterns among the main Hawaiian Islands, and provide evidence for a new Hawaiian Chryscodracon species using molecular data. Evidence suggests that there was an initial colonization of the islands to Kauai or Maui, or both concurrently, followed by dispersal and speciation in the other islands.