PHYLOGENETIC STRUCTURE IN THE GRASS FAMILY (POACEAE) AS INFERRED FROMCHLOROPLAST DNA RESTRICTION SITE VARIATION

A cladistic analysis of chloroplast DNA restriction site variation amo ng representatives of all subfamilies of the grass family (Poaceae), u sing Joinvillea (Joinvilleaceae) as the outgroup, placed most genera i nto two major clades. The first of these groups corresponds to a broad ly circumscribed subfamily Pooideae that includes all sampled represen tatives of Ampelodesmeae, Aveneae, Brachypodieae, Bromeae, Diarrheneae , Meliceae, Poeae, Stipeae, and Triticeae. The second major clade incl udes all sampled representatives of four subfamilies (Panicoideae [tri bes Andropogoneae and Paniceae], Arundinoideae [Arundineae], Chloridoi deae [Eragrostideae], and Centothecoideae [Centotheceae]). Within this group (the ''PACC'' clade), the Panicoideae are resolved as monophyle tic and as the sister group of the clade that comprises the other thre e subfamilies. Within the latter group, Danthonia (Arundinoideae) and Eragrostis (Chloridoideae) are resolved as a stable monophyletic group that excludes Phragmites (Arundinoideae); this structure is inconsist ent with the Arundinoideae being monophyletic as currently circumscrib ed. The PACC clade is placed within a more inclusive though unstable c lade that includes the woody Bambusoideae (Bambuseae) plus several dis parate tribes of herbaceous grasses of uncertain affinity that are oft en recognized as herbaceous Bambusoideae (Brachyelytreae, Nardeae, Oly reae, Oryzeae, and Phareae). Among eight most-parsimonious trees resol ved by the analysis, four include a monophyletic Bambusoideae sensu la to (comprising Bambuseae and all five of these herbaceous tribes) as t he sister group of the PACC clade; in the other four trees these bambu soid elements are not resolved as monophyletic, and the PACC clade is nested among these tribes. These results are consistent with those of previous analyses that resolve a basal or near-basal branch within the family between Pooideae and all other grasses. However, resolution by the present analysis of the PACC clade, which includes Centothecoidea e, Chloridoideae, and Panicoideae, but excludes Bambusoideae, is incon sistent with the results of previous analyses that place Bambusoideae and Panicoideae in a monophyletic group that excludes Centothecoideae and Chloridoideae.