Phylogeny of Cleome L. and its close relatives Podandrogyne Ducke and Polanisia Raf. (Cleomoideae, Cleomaceae) based on analysis of nuclear ITS sequences and morphology

Abstract

A phylogenetic survey of representatives from all New World and several Old World supraspecific groupings of Cleome, as well as from the closely related Podandrogyne and Polanisia, was conducted based on separate analysis of nuclear ribosomal ITS sequences and of morphological characters. Parsimony analysis of the molecular data recognized this group of cleomoid taxa as a strongly supported monophyletic lineage. Podandrogyne was imbedded within a highly supported Andinocleome clade, whereas Polanisia was placed as a member of a North American/Old World Cleome s. l. clade but with low support. The ITS data also indicated the sequential divergence of several basal Old World (sects. Cleome, Gymnogonia, Ranmanissa and Rutidosperma) and North American (subg. Physospermon, sect. Peritoma) lineages followed by more recent splittings of Central and South American lineages (the Andinocleome (sects. Pterosperma and Rimosperma) group, and sects. Melidiscus and Tarenaya). The morphological data showed extensive homoplasy and did not resolve the phylogeny of these cleomoids, although the cladistic analysis distinguished two poorly supported (subg. Eucleome and sect. Tarenaya) clades. Despite this, several sets of morphological and chromosomal secondary synapomorphies served to characterize the main sectional clades recovered in the molecular tree. Based on the strong support of the Cleome + Podandrogyne + Polanisia clade and the insufficient resolution and low support of the basal branches of this tree, and on the inherent homoplasy and unsatisfactory resolution of the morphological diagnostic traits used to characterize these taxa, a reunification of the three cleomoid genera under a large genus Cleome s. l. would be advisable. A biogeographical interpretation of our molecular phylogeny indicated and earlier origin of the ancestral Cleome lineages in the Old World, followed by colonization of North America and then a subsequent expansion towards central and South American with more recent secondary radiations in these subcontinents.