A PHYLOGENETIC ANALYSIS OF CHLOROPLAST DNA RESTRICTION SITE VARIATION IN POACEAE SUBFAM POOIDEAE

A phylogenetic analysis was conducted on chloroplast DNA restriction site variation in 34 genera of grasses (family Poaceae), including 28 genera from subfam. Pooideae (representing tribes Aveneae, Brachypodieae, Bromeae, Meliceae, Poeae, Stipeae, and Triticeae) and representatives of three other subfamilies, Arundinoideae, Oryzoideae, and Panicoideae. Analyses of all 34 genera always distinguished Pooideae as monophyletic, regardless of which nonpooid genus functioned as outgroup; six separate analyses of all 28 pooid genera, each including one of the six nonpooid genera as outgroup, resolved five identically-constituted clades within Pooideae (in four cases), or (in the other two cases) yielded results that were less well resolved, but not in conflict with those of the other four analyses. The four best-resolved analyses distinguished Meliceae as the earliest diverging lineage within Pooideae, and Stipeae as the next. Above the point of divergence of Stipeae is a dichotomy between supertribe Triticodae (including tribes Brachypodieae, Bromeae, and Triticeae), and a clade comprising Poeae and Aveneae. The analysis supports some tribal realignments, specifically the assignment of Briza, Chascolytrum, Microbriza, and Torreyochloa to Aveneae, and Arctagrostis, Catabrosa, and Sesleria to Poeae. The analysis also suggests that the pooid spikelet (i.e., glumes shorter than lemmas and florets two or more) is plesiomorphic in Pooideae, and that spikelets with one floret, and those with glumes longer than the first lemma, each have evolved more than once within Pooideae. Results also indicate that small chromosomes and chromosome numbers based on x=c. 10-12 are plesiomorphic within Pooideae. Alternative states of these characters (chromosomes large, chromosome numbers based on x=7) are interpreted as synapomorphies or parallelisms of clades that include Triticodae, Aveneae, and Poeae. Lanceolate lodicule shape may be a synapomorphy of the clade that includes Stipeae, Triticodae, Aveneae, and Poeae, and loss of lodicule vascularization a synapomorphy of the entire Pooideae. © 1990 Springer-Verlag.