A PHYLOGENY OF THE GRASS FAMILY (POACEAE) BASED ON NDHF - SEQUENCE DATA

DNA sequences were generated for the chloroplast gene ndhF to address phylogenetic relationships among the major lineages of the Poaceae. Ou r primary objectives were: 1) to test the monophyly of the Bambusoidea e s.l., which traditionally has been viewed as the ancestral lineage o f the family, and 2) to resolve phylogenetic relationships between dis parate elements of this subfamily and the other major grass clades. A total of 45 grass sequences and two outgroup sequences were analyzed u sing parsimony and distance-based phylogenetic reconstruction methods. Two tribes of neotropical herbaceous bamboos, the Streptochaeteae and Anomochloeae, are resolved as the most basal clade within the family, with a clade representing the pantropical Phareae, also regarded as h erbaceous bamboos, as the next most basal lineage. These results confi rm that certain elements within the Bambusoideae s.l. are basal within the family and contrast with previous hypotheses that the Pooideae re present a basal or near-basal branch. Exclusive of the basal lineages of herbaceous bamboos, the remainder of the family formed a monophylet ic clade with two primary subdivisions, a weakly supported ''BOP'' cla de (bambusoids, oryzoids, and pooids), and a strongly supported PACC c lade (panicoids, arundinoids, chloridoids, and centothecoids). Each of the three lineages of the BOP clade is well supported. The Bambusoide ae s.l. and Arundinoideae are polyphyletic, and the inclusion of Thysa nolaeneae and Centotheceae in a more broadly defined Panicoideae is su pported. The Pooideae s.l. and Chloridoideae are resolved as monophyle tic. The ancient evolutionary divergence within the Poaceae and the ot her relationships suggested by the phylogenetic analyses indicate that reevaluation of intrafamilial classification is necessary.