Molecular phylogeny of the genus Corchorus (Grewioideae, Malvaceae s.l.) based on nuclear rDNA ITS sequences

Abstract

A molecular phylogenetic analysis of the genus Corchorus (Grewioideae, Malvaceae s.l.) is presented, based on sequences of the nuclear ribosomal DNA internal transcribed spacer (ITS) region for 144 accessions representing 47 species. Several other genera from the subfamily Grewioideae, namely Pseudocorchorus, Triumfetta, Sparrmannia, Entelea, and Grewia, were included as outgroups. The monophyly of the genus was well supported by all phylogenetic analyses (maximum likelihood, Bayesian approaches, and parsimony), and Corchorus was divided into four major clades. The majority of African species formed a statistically highly supported and distinct clade separated from the other pantropically distributed species. Several endemic species from Australia, New Caledonia, and tropical America were nested within this distinct clade, indicating dispersal from Africa to the rest of the pantropics. Based on the taxa included in this study, the two cultivated species (C. olitorius and C. capsularis) shared a common ancestry with wild species of C. africanus, C. brevicornatus, C. pseudocapsularis, C. pseudo-olitorius, C. urticifolius, C. pilosus, C. orinocensis, and C. cunninghamii. Pseudocorchorus, previously considered an accepted genus, was nested within the genus Corchorus and shared a common ancestry especially with C. depressus and C. siliquosus. Based on morphological and anatomical similarity as well as the results of the present molecular findings, inclusion of the six Pseudocorchorus species into Corchorus is proposed, with Pseudocorchorus as a synonym of Corchorus. Of the included outgroup taxa, Triumfetta is the closest sister to Corchorus, while the common ancestor of Corchorus/Pseudocorchorus, Triumfetta, Sparrmannia, and Entelea is Grewia. A further phylogenetic study with more taxa mainly from Australia, together with additional molecular markers and morphological investigation, would help to test the hypothesis on the biogeography and growth form evolution of the genus Corchorus. Keywords: Corchorus, Jute, Malvaceae s.l., Phylogeny, Pseudocorchorus