Relationships among the subfamilies of the grasses (Poaceae). GRASS PHYLOGENY WORKING Group

GIUSSANI, L., HASENSTAB-LEHMAN, K., HILU, K.W., HODKINSON, T.R., INGRAM, A.L., KELLOGG E.A., MASHAYEKHI, S., MORRONE, O., OSBORNE, C.P., SALAMIN, N., SCHAEFER, H., SPRIGGS, E., SMITH, S.A., ZULOAGA

St. Louis

Congreso; Botany 2011. Healing the planet; 2011

ASPT, Botanical Society of America, etc

The phylogeny of the grass family has received a great deal of attention, and published data to date have supported twelve well-supported clades that are named as subfamilies.  The three smallest subfamilies are consistently supported as successive sisters to the remainder, which are divided into the BEP clade (Bambusoideae, Ehrhartoideae and Pooideae) and the PACMAD clade (Panicoideae, Arundinoideae, Chloridoideae, Micrairoideae, Aristidoideae and Danthonioideae).   Both the BEP clade and the PACMAD clade are strongly supported groups, but relationships among the subfamilies within them are unresolved.   Phylogenetic analyses using one or two genes have found almost all possible resolutions of the subfamilies, and the results are often highly sensitive to taxon sampling.   The PACMAD clade is of particular interest because it contains at least 17 origins (and possible reversals) of C4 photosynthesis, but determining the precise number and phylogenetic position of these changes requires a resolved phylogeny.  The GPWGII was formed in 2010 specifically to resolve the PACMAD phylogeny to be able to investigate C4 evolution.  By using data available in NCBI and supplementing it with extensive unpublished data from each of our lab groups, we were able to assemble a dataset of 318 taxa with sequences from the chloroplast loci rcbL, ndhF and matK.  Additional sequences were then produced to fill in gaps in the matrix, so we now have a data set with only 8% missing data, in which most taxa have sequences of all three loci.   Within the PACMAD clade, our data support the position of Aristidoideae as sister to the other subfamilies, and Panicoideae as the next diverging clade.  The remaining four taxa have the relationship ((chloridoid, danthonioid),(arundinoid, micrairoid)).   Although not a focus of this particular project, we also resolved the BEP clade as ((bambusoid, pooid), oryzoid).    Our taxon sampling focused particularly on Panicoideae, for which we included nearly all currently-recognized genera.   Our results are consistent with previous single-gene studies, but better resolved and with stronger support.