The commelinoid monocots (sensu APG 1998) comprise four large orders (Arecales, Commelinales, Poales and Zingiberales) and several taxa of uncertain affinity. They include some of the largest flowering-plant families and encompass an incredible array of ecological and morphological diversity. Recent taxonomic treatments and molecular studies have greatly clarified the circumscription of the commelinoids and constituent orders, but many aspects of relationship in the group remain poorly resolved at the family level and above. We present results from an ongoing study of higher-order relationships in the commelinoids, based on analysis of ~13.5 kb (unaligned) of DNA sequence data per taxon, for 13 taxa in ten families. The regions sampled include atpB, rbcL, ndhF, ten photosystem II genes, two ndh genes, three ribosomal protein genes, three introns and two intergenic spacer regions. Parsimony-based bootstrap analyses (using the Fitch parsimony criterion) robustly support commelinoid monocot monophyly, although several major taxa have not yet been sampled, including Arecales. The position of the family Dasypogonaceae was not fully resolved, but it is clearly isolated from Commelinales, Zingiberales and Poales. Zingiberales is strongly supported as the sister-group of the Commelinales. Our results support the inclusion of Hanguanaceae in Commelinales, as was recently proposed by Chase et al. 2000, although the monophyly of the redefined Commelinales (Commelinaceae, Hanguanaceae, Haemodoraceae, Philydraceae and Pontederiaceae) was only weakly supported. Within the Commelinales, Haemodoraceae and Pontederiaceae were strongly supported as sister taxa, as were Commelinaceae and Hanguanaceae. Philydraceae was moderately well supported as the sister-group of Haemodoraceae-Pontederiaceae. We also address the identity of the sister-group of the commelinoids, and discuss various aspects of the molecular evolution of the regions examined.

Key words: chloroplast phylogeny, Commelinales, Commelinoids, Hanguana, large-scale data