Phylogenetic analyses of rbcL sequence data from grasses are presented, extending the work of an earlier study. Based on molecular evidence that Joinvilleaceae and Restionaceae are closely allied to Poaceae, species from these families and from a distantly related dicot were variously employed as outgroups and analyzed with 23 species of Poaceae using the parsimony method. Measures of support were determined. The terminal portion of the tree was invariant in all analyses. Outgroup selection affected the basal topology of the tree with somewhat different measures of support for the deeper branches of the tree. When the outgroup was the dicot, pooid grasses made up the basal clade. When the outgroup was Joinvilleaceae or Restionaceae, species of Bambusoideae were basalmost. Increased sampling did not result in a marked increase in support of the rbcL data for the earliest branching events.