Generic delimitation of Hopea Roxb. and Shorea Roxb. ex. C.F. Gaertn. (Dipterocarpaceae) : molecular and morphological evidence

Abstract

The two largest genera in the Dipterocarpaceae, Hopea and Shorea, have many similarities and exhibit continuous morphological variation at both the generic and specific levels and they are regarded as closely related genera (Ashton, 1982). The many similarities between the two genera leave very few discrete characters to separate them. The single and most conspicuous morphological character distinguishing the two genera is the comparative development of the fruit calyx. Hopea is characterised by two long and three short fruit calyx wings, while Shorea has three long and two short wings on the fruit (Ashton, 1982). This study investigated the phylogenetic relationship of Hopea and Shorea to address the issue of their generic delimitation. Observations and measurements were made of morphological characters, and DNA sequences were obtained for the trnL-F region of the chloroplast and the ITS region of the nuclear genome. Cladistic analyses were performed on a dataset of 40 selected morphological characters, categorised as either quantitative or qualitative. These analyses enabled the construction of a putative phylogeny of Hopea and Shorea, and the characters that define each genus were identified and examined. A detailed study of the inflorescence structure of som selected Dipterocarpaceae species was also carried out. The inflorescence was parsed into hierarchical nested units and the characters obtained were incorporated into the cladistic analyses. Several analyses were performed to test the effect of different parts ofthe data set on the robustness of the resultant topologies. Results from the morphological study showed that neither Hopea nor Shorea are monophyletic genera. Analyses of the molecular data sets were performed to infer phylogenetic relationships using independent sources of evidence, the chloroplast and nuclear genomes. Analyses that examined the effect of insertion-deletion events and of different putative outgroups on the robustness of the resultant topologies were also performed. The results suggested that Hopea is probably a monophyletic genus (albeit with some minor recircumscription) while Shorea is clearly non-monophyletic. Since the study used two independent data sets-morphological and molecular-a combined analysis using both was also performed. This combination of data provided a better insight into the relationships of Hopea and Shorea. Results from this analysis were largely similar to those obtained from analyses of molecular data. Show more