Fig. 4.

Dating of taxonomic radiation within subclades of the grass family (Poaceae) by using fossil phytoliths (this study) and macrofossils (23–26). Approximate ages for basal nodes (marked with an open circle; 95% confidence intervals not shown) are provided by molecular clock analysis (5). (A) Phylogeny in which the BEP clade is sister to the PACCAD clade (10). (B) Phylogeny in which the Pooideae is sister to the PACCAD grasses (30). The shift to open habitats could have occurred once or twice. Open shapes, openhabitat grass clades; black shapes with white dots and all other terminal taxa, closed-habitat grasses; “OPEN HABITAT,” shift to open habitats; *, except Brachyelytrum.