Format: ORAL

Robert J. Soreng1*, Timothy J. Gallaher2, Paul M. Peterson1, Konstantin Romaschenko1, Fernando O. Zuloaga3, De-Zhu Li4,5, Lynn G. Clark6, Christopher D. Tyrrell7, Cassiano A. D. Welker8, Elizabeth A. Kellogg9, Jordan K. Teisher10

1 Department of Botany, MRC-166, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013-7012, USA 2 Department of Natural Science, Herbarium Pacificum, Bishop Museum, 1525 Bernice St., Honolulu, HI 96817, USA 3 Instituto de Botánica Darwinion (CONICET-ANCEFN), Labardén 200, Casilla de Correo 22, San Isidro B1642HYD, Buenos Aires, Argentina 4 Germplasm Bank of Wild Species, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China 5 University of Chinese Academy of Sciences, Beijing 100049, China 6 Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA 50011, USA 7 Botany Department, Milwaukee Public Museum, 800 W Wells Street, Milwaukee, WI 53233, USA 8 Instituto de Biologia, Universidade Federal de Uberlândia, Rua Ceará s/n, 38400-902, Uberlândia, MG, Brazil 9 Donald Danforth Plant Science Center, St Louis, MO 63132, USA 10 Missouri Botanical Garden, 4344 Shaw Blvd, St. Louis, MO 63110, USA2Department of Natural Science, Herbarium Pacificum, Bishop Museum, 1525 Bernice St., Honolulu, HI 96817, USA

Grasses are widespread on every continent and occur in all terrestrial biomes. The dominance and spread of grasses and grassland ecosystems led to significant changes in Earths climate, geochemistry, and biodiversity. Abundant chloroplast DNA sequence data, and advances in placing grass fossils within the family allow for phylogenetic reappraisal of the familys origins, timing, geographic spread, and factors promoting diversification. We constructed a time-calibrated grass phylogeny and inferred ancestral areas using chloroplast DNA sequences from nearly 90% of extant grass genera. With a few notable exceptions, the phylogeny is well resolved to the subtribal level and in agreement with our current classification. Using this phylogenetic, temporal, and spatial framework, we review the evolution and biogeography of the family and present biogeographical hypotheses concerning its origins, evolutionary tempo, and diversification. Extant lineages of the family began to diversify around the Late/Early-Cretaceous boundary (crown 98.54 Ma) in West Gondwana. All subfamily crowns (except Pharoideae) evolved between the Late-Cretaceous to Late-Eocene, with most tribe crowns between Mid-Eocene to Early-Oligocene, and stems of most genera between the Mid-Oligocene and Late-Miocene. The splitting of Gondwana appears responsible for the initial vicariance of Anomochlooideae from the rest of the family: Its genera lack true spikelets and are endemic to and the only subfamily (or tribe) with a crown (80 Ma) in South America. Africa was the center of origin for much of the early diversification of the family (Spikelet and Bistigmatic clades, Puelioideae, Core-Grass-clade, BOP and Oryzoideae, PACMAD and ACMAD clades, Panicoideae, Aristidoideae, Arundinoideae, and Chloridoideae). Bambusoideae and Micrairoideae exhibit Indomalayan origins. Pooideae and tribes exhibit Palearctic origins. Ehrhartoideae and Cyperochloeae are tribes of Australian origins. No tribes have North American origins. Key questions to answer are the roles of Antarctica, extinction, unequal-rates of sequence evolution (woody-bamboos, and annuals), and whether Aristidoideae or Panicoideae evolved first.