Systematics of Portulaca L. (Portulacaceae), including its position within suborder Cactineae (order Caryophyllales).

摘要

The genus Portulaca L. comprises ca. 100 species distributed worldwide, mainly in the tropics and subtropics, with centers of diversity in South America and Africa, and is the only member of the recently recircumscribed Portulacaceae (other genera are now in Anacampserotaceae, Montiaceae, and Talinaceae). The most recent taxonomic study of Portulaca at a worldwide scale was done 40 years ago, and there are no published phylogenetic studies focused on the genus. At a higher taxonomic level, relationships of Portulaca with Anacampserotaceae, Cactaceae, and Talinaceae are uncertain, although in analyses of chloroplast, mitochondrial, and nuclear DNA sequences they form a strongly supported monophyletic group (ACPT clade) within suborder Cactineae (Caryophyllales). Chapter 1 focused on relationships within Cactineae. Three chloroplast markers (rpl14-rps8-infA-rpl36 region, atpI-atpH intergenic spacer, ndhA intron) were analyzed. The resulting phylogenetic hypotheses were consistent with previous studies in obtaining high support for the monophyly of the suborder and the ACPT clade, but relationships otherwise remain uncertain. Divergence times analysis estimated the age of Cactineae ca. 20 million years (My). The evolution of photosynthetic pathways was studied (based on leaf anatomy and carbon isotope ratios). C 3 photosynthesis is inferred as ancestral. CAM evolved multiple times. C4 evolved once from C3 in Portulacaceae. Historical biogeography reconstruction showed that Cactineae are of North American origin, although outgroup selection may have biased this result. Chapters 2 and 3 focused on Portulaca. Relationships within Portulaca were studied using nuclear (ITS) and chloroplast (ndhF, psbD-trnT intergenic spacer, ndhA intron) markers. Divergence times, character evolution (including some characters that have been used for infrageneric taxonomy), and historical biogeography were studied. Portulaca is strongly supported as monophyletic, with two main clades also highly supported. The genus was estimated to be ca. 15 My old and originated in South America. Existing infrageneric classifications are only partially supported by the phylogenetic estimate, thus a new classification based on the molecular phylogenies, morphology, and anatomy is proposed. Unlike all other Portulaca species studied, P. cryptopetala was discovered to have non-Kranz anatomy and undergo C3 photosynthesis. When considered in a phylogenetic context, these traits represent reversals from Kranz anatomy and C4 photosynthesis.