Robust Inference of Monocot Deep Phylogeny Using an Expanded Multigene Plastid Data Set

Abstract

We use multiple photosynthetic, chlororespiratory, and plastid translation apparatus loci and their associated noncoding regions (ca. 16 kb per taxon, prior to alignment) to make strongly supported inferences of the deep internal branches of monocot phylogeny. Most monocot relationships are robust (an average of ca. 91% bootstrap support per branch examined), including those poorly supported or unresolved in other studies. Our data strongly support a sister-group relationship between Asparagales and the commelinid monocots, the inclusion of the orchids in Asparagales, and the status of Petro- saviaceae as the sister group of all monocots except Acorus and Alismatales. The latter finding supports recognition of the order Petrosaviales. Also strongly supported is a placement of Petermannia disjunct from Colchicaceae (Liliales) and a sister-group relationship between Commelinales and Zingiberales. We highlight the remaining weak areas of monocot phylogeny, including the positions of Dioscoreales, Liliales, and Pandanales. Despite substantial variation in the overall rate of molecular evolution among lineages, inferred amounts of change among codon-position data partitions are correlated with each other across the monocot tree, consistent with low incongruence between these partitions. Cerato- phyllum and Chloranthaceae appear to have a destabilizing effect on the position of the monocots among other angiosperms; the issue of monocot placement in broader angiosperm phylogeny remains problematic.