An unusual new species of Trevesia from Vietnam and its implications on generic delimitation in Araliaceae

Trevesia vietnamensis J. Wen & P.K. L?c (Araliaceae) is described as an unusual new species from northwestern Vietnam. This species has 4?5-merous flowers with a 4-5-locular ovary and palmately compound leaves and would thus fit well within Brassaiopsis morphologically. Phylogenetic analysis using the nuclear ribosomal ITS and the chloroplast ndhF and trnL-F sequences, however, clearly places the new taxon in Trevesia, defined to include species with 6-16-merous flowers with 6-16-locular ovaries, and palmately lobed simple leaves. The discovery of Trevesia vietnamensis thus blurs the generic boundary between Trevesia and Brassaiopsis. The phylogenetic analysis suggests a sister-species relationship between Trevesia vietnamensis and T. lateospina from northern Thailand, a finding supported by a shared morphological character?the presence of setose hairs on the inflorescences and young stems. Trevesia vietnamensis is restricted to two localities in northwestern Vietnam. It grows in limestone areas in valleys and on shady mountain slopes at 500-700 m in primary, tropical, monsoon, broad-leaved forests.