Polyphyly of Arundinoideae (Poaceae) and awn evolution in the grasses

The sub-family Arundinoideae represents one of the last unsolved taxonomic mysteries in the grass family (Poaceae) due to the narrow and remote distributions of many of its 19 morphologically and ecologically heterogeneous genera. Resolving the phylogenetic relationships of these genera could have substantial implications for understanding character evolution in the grasses, for example the twisted geniculate awn – a hygroscopic awn that has been shown to be important in seed germination for some grass species.

Teisher et al. conducted a phylogenetic analysis on a matrix of full-plastome sequences from 123 species in 107 genera representing all grass subfamilies, with 15 of the 19 genera in subfamily Arundinoideae. They then used parsimony and maximum likelihood mapping approaches to estimate ancestral states to explore the evolutionary history of the twisted geniculate lemma awn.

Arundinoideae is found not to be a naturally occurring group, with members that are more closely related to species in other subfamilies. The twisted geniculate lemma awn has evolved at least seven times independently in the grasses.