PHYLOGENY OF POACEAEINFERRED FROM matKSEQUENCES'Khidir W. Hilu2, Lawrence A. Alice2',and Hongping Liang2ABSTRACT Complete sequences of the plastid gene rnatK were determined for 62 species of Poaceae from 60 genera. 26 tribes.and nine subfamilies to infer phylogenetic relationships. Restio tetraphyllus (Restionaceae) and Joinvillea ascendens(Joinvilleaceae) were used as outgroups. Cladistic analysis using PAUP yielded 39 most parsimonious trees with severalwell-supported major lineages. The strict consensus tree shows Streptochaeta and Annomochloa forming the two mostbasal lineages in grasses, followed by Pharus being sister to the remaining species. The other grasses divide into threeclades: (1) subfamily Bambusoideae (excluding Brachyelytrum) plus Pooideae; (2) Oryzoideae: and (3) subfamiliesPanicoideae, Arundinoideae, Centothecoideae, and Chloridoideae (termed PACC). Except for Arundinoideae, monophylyof each PACC subfamily is generally well supported; however, relationships among subfamilies are unresolved or weaklysupported. Results obtained using matK sequences are largely consistent with other phylogenies based on molecularand structural data. particularly in that relationships among subfamilies remain unclear. Interest in the evolution of grasses began earlyin this century with proposed hypotheses based onassessment of existing knowledge of the family(e.g., Bew, 1929; Hubbard, 1948; Stebbins, 1956,1982; Prat, 1960; Clayton, 1981; Tsvelev, 1983).Empirical approaches to phylogenetic reconstruc-tion of the Poaceae followed those initial hypothe-ses, starting with cladistic analyses of morphologi-cal and anatomical characters (Baum, 1987;Kellogg & Campbell, 1987; Kellogg & Watson,1993). Recently, molecular data have provided thegrounds for phylogenetic hypotheses in grasses atthe subfamilial and tribal levels. These studieswere based on information from chloroplast DNA(cpDNA) restriction sites and DNA sequencing ofthe rhcL, ndhF, rps4, rpoC2, matK, nuclear ribo-somal DNA (nrDNA) 18S and 26S, phytochrome,and granule-bound starch synthase genes, as wellas the noncoding nrDNA Internai TranscribedSpacer (ITS) region (Hamby & Zimmer, 1988; Doe-bley et al., 1990; Davis & Soreng, 1993; Cummingset al., 1994; Hsiao et al., 1994; Nadot et al., 1994;Barker et al., 1995, 1999; Clark et al., 1995; Du-vall & Morton, 1996; Liang & Hilu, 1996; Mathews& Sharrock, 1996; Mason-Gamer et al., 1998; So-reng & Davis, 1998; Hsiao et al., 1999). Although these studies have refined our under-standing of grass evolution at the subfamilial leveland, to a certain degree, at the tribal level, majorquestions remain to be resolved. Although the basalpositions of Anomochloeae, Phareae, and Strepto-chaeteae have been established, their relativeplacement and taxonomic status are debatable. Un-certainties also exist concerning the phylogeneticaffinities among subfamilies and the taxonomicrank of others such as the Oryzoideae. In this study, the chloroplast matK gene was cho-sen to address these and other questions pertainingto higher-level grass systematics. The matK gene is-1515 base pairs (bp) in most angiosperms, locat-ed within the trnK intron, and functionally may beinvolved in splicing group II introns (Neuhaus &Link, 1987; Ems et al., 1995; Hilu & Alice, inpress a). The effective application of this gene inplant systematics (e.g., Johnson & Soltis, 1994,1995; Hilu & Liang, 1997; Kron, 1997) and grasses(Liang & Hilu, 1996; Hilu & Alice, in press a, b)has already been documented. matK is known tohave relatively high rates of substitution comparedto other chloroplast genes (see Olmstead & Palmer,1994; Johnson & Soltis, 1995). This gene exhibitsa relatively high proportion of transversions, andthe 3' region of its open reading frame (ORF) has ' We thank Nigel Barker, lynn Clark, Travis Columbus, Jerry Davis, Tarciso Filgueiras, Gary Fleming, Surrey Jacobs.David Knepper, A. Nishiwaki, John Randall. Thomas Wieboldt. the Botanical Garden at Bonn, and the MissouriBotanical Garden for supplying DNA or plant samples. Seed material for some accessions was kindly provided by theU.S. Department of Agriculture. Agriculture Research Service-National Plant Germplasm System. We also thank Ger-asimo Borneo, Thomas Borsch. Gerrit Iavidse. John MacDougal, and Christoph Neinhuis for their assistance. Thiswork was supported bv NSF grant #DEB-9634231 and Sigma Xi. 2 Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg. Virginia 2406(-1-0406. U.S.A. SCurrent address: Department of Biology, Western Kentucky University, Bowling Green. Kentucky 42101, U.S.A.ANN. MIssouRI BOT. GARD. 86: 835-851. 1999.