PHYLOGENETICS AND CHARACTER EVOLUTION IN THE GRASS FAMILY (POACEAE) -SIMULTANEOUS ANALYSIS OF MORPHOLOGICAL AND CHLOROPLAST DNA RESTRICTION SITE CHARACTER SETS

A phylogenetic analysis of the grass family (Poaceae) was conducted us ing two character sets, one representing variation in 364 mapped and c ladistically informative restriction sites from all regions of the chl oroplast genome, the other representing variation in 42 informative '' structural characters.'' The structural character set includes morphol ogical, anatomical, chromosomal, and biochemical features, pins struct ural features of the chloroplast genome. The taxon sample comprises 75 exemplar taxa, including 72 representatives of Poaceae and one repres entative of each of three related families (Flagellariaceae, Restionac eae, and Joinvilleaceae); Flagellaria served as the outgroup for the p urpose of cladogram rooting. Among the grasses, 24 tribes and all 16 s ubfamilies of grasses recognized by various modern authors were sample d. Transformations of structural characters are mapped onto the phylog enetic hypotheses generated by the analysis, and interpreted with resp ect to biogeography and the evolution of wind pollination in the grass family A major goal of the study was to test the monophyly of several putatively natural groups, including Bambusoideae, Pooideae, Arundino ideae, and the ''PACC clade'' (the latter comprising subfamilies Panic oideae, Arundinoideae, Chloridoideae, and Centothecoideae), as well as to analyze the phylogenetic structure within these groups and others. Several genera of controversial placement (Amphipogon, Anisopogon, An omochloa, Brachyelytrum, Diarrhena, Eremitis, Ehrharta, Lithachne, Lyg eum, Nardus, Olyra, Pharus, and Streptochaeta) also were included, wit h the goal of determining their phylogenetic affinities. The two chara cter sets were analyzed separately, and a simultaneous analysis of the combined matrices also was conducted. The combined data set also was analyzed using homoplasy-implied weights. Among major results of the c ombined unweighted analysis were resolution of a sister-group relation ship between Joinvillea and Poaceae; resolution of a clade comprising Anomochloa and Streptochaeta as the sister of all other grasses, with Pharus the next group to diverge from the lineage that includes all re maining grasses; and resolution of other taxa often assigned to Bambus oideae s.l. (including Ehrharta and Oryzeae, and excluding a few other taxa as noted) as a paraphyletic assemblage, within which is nested a clade that consists of Brachyelytrum, the PACC clade (including Amphi pogon), and Pooideae (including Brachypodieae, Stipeae, Anisopogon, Di arrhena, Lygeum, and Nardus). Within the PACC clade, Aristida is ident ified as the sister of all other elements of the group; Chloridoideae, Centothecoideae, and Panicoideae are each resolved as monophyletic, t he latter two being sister-groups; and the remaining Arundinoid elemen ts constitute a paraphyletic group within which are nested these three subfamilies. Within the Pooideae, four ''core tribes'' (Bromeae, Hord eeae [i.e., Triticeae], Agrostideae [i.e., Aveneae], and Poeae, the la tter including Sesleria) are resolved as a monophyletic group that is nested among the remaining elements of the subfamily (Brachypodieae, M eliceae, Stipeae, Anisopogon, Diarrhena, Lygeum, and Nardus). A second principal goal of the analysis was to identify structural synapomorph ies of clades. Among the synapomorphies identified for some of the maj or clades are the following: gain of a 6. 4 kb inversion in the chloro plast genome in Joinvillea and the grasses; reduction to 1 ovule per p istil, gain of a lateral ''grass-type'' embryo, and gain of an inversi on around the gene trnT in the chloroplast genome in the grasses; loss of arm cells in the clade that consists of Brachyelytrum, Pooideae, a nd the PACC clade; loss of the epiblast and gain of an elongate mesoco tyl internode in the PACC clade; gain of proximal female-sterile flore ts in female-fertile spikelets, gain of overlapping embryonic leaf mar gins, and gain of Panicum-type endosperm starch grains in the clade th at comprises Centothecoideae and Panicoideae; and loss of the scutella r tail of the embryo in Pooideae (in one of two alternative placements of Pooideae among other groups). These findings are consistent with a n origin and early diversification of grasses as forest understory her bs, followed by one or more radiations into open habitats, concomitant with multiple origins of C-4 photosynthesis and specialization for wi nd pollination.