Molecular and Micromorphological Evidence for the Taxonomic Differentiation of the Jamaican Endemic Genus Dendrocousinsia Millsp. (Euphorbiaceae)

With seven species, Dendrocousinsia (Euphorbiaceae) is the most species-rich genus of seed plants endemic to Jamaica. Fast-evolving nuclear molecular markers (ETS and ITS regions of the nuclear ribosomal DNA) and leaf anatomical traits were investigated to understand the evolution and systematics of this genus. Phylogenetic analyses based on maximum parsimony and Bayesian inference found little nucleotide variation, suggesting rapid speciation across different ecosystems of the island. Bayesian analyses supported a sistership between D. crenulata and D. fasciculata. Furthermore, D. alpina and D. crenulata displayed relatively long branches. Transverse sections through the main vein of preserved leaves from seven species of Dendrocousinsia and Sebastiania hexaptera highlight micromorphological similarities between D. elliptica and S. hexaptera, as both exhibited two to three layers of collenchyma cells parallel to the vascular bundle, below the adaxial epidermal layer and above the abaxial epidermal layer. The outgroup species, S. hexaptera, and three Dendrocousinsia taxa (i.e. D. crenulata, D. fasciculata, and D. lesteri var. lesteri) share the presence of few air spaces in the spongy mesophyll. Analysis of the epidermal cells of the leaves reveal significant variation in these cells and the arrangement of vascular bundles in all species examined.