A revision of the genus Croton (Euphorbiaceae) in Sumatra (Indonesia).

Croton (Euphorbiaceae) is a very large genus of over 1 200 species of herbs, shrubs and trees occurring mainly in the (sub)tropics. The major diversity of Croton is within the Neotropics; and there are comparatively few species in South-East Asia. This contribution provides a revision of Croton from the Sumatran region in Indonesia, including descriptions and a determination key. In total sixteen species are recognized for Sumatra, including four species new to science, C. beccarii, C. scalaeus, C. simalurensis, and C. viridifolius. Two new synonyms and lectotypification of numerous names are also included. Besides a taxonomic treatment, a molecular analysis, using the nuclear ribosomal internal transcribed spacer (ITS), based on former data extended with Sumatran species, was performed to create a phylogeny that places the Sumatran species in a phylogenetic context. In total 13 new sequences were created, which were combined with 56 sequences obtained from GenBank. The results from the phylogenetic analysis, based on Bayesian inference, are in line with the phylogeny as published for mainly the Australian species of Croton by Van Ee et al. (2015). [ABSTRACT FROM AUTHOR]