Family: Poaceae |
Mary E. Barkworth Plants usually perennial; usually tightly to loosely cespitose, sometimes rhizomatous. Culms annual or perennial, not woody, branches 1 to many at the upper nodes. Leaves basally concentrated to evenly distributed; sheaths open, margins not fused, sometimes ciliate distally, basal sheaths sometimes concealing axillary panicles (cleistogenes), sometimes wider than the blade; collars sometimes with tufts of hair at the sides extending to the top of the sheaths; auricles absent; ligules scarious, often ciliate, cilia usually shorter than the base, ligules of the lower and upper cauline leaves sometimes differing in size and vestiture; pseudopetioles absent; blades linear to narrowly lanceolate, venation parallel, cross venation not evident, cross sections non-Kranz, without arm or fusoid cells; epidermes of adaxial surfaces sometimes with unicellular microhairs, cells not papillate. Inflorescences usually terminal panicles, occasionally reduced to racemes in depauperate plants, sometimes 2–3 panicles developing from the highest cauline node. Spikelets usually with 1 floret, sometimes with 2–6 florets, laterally compressed to terete; rachillas not prolonged beyond the base of the floret in spikelets with 1 floret, prolonged beyond the base of the distal floret in spikelets with 2–6 florets, prolongation hairy, hairs 2–3 mm; disarticulationabove the glumes and beneath the florets. Glumes usually exceeding the floret(s), always longer than 1/4 the length of the adjacent floret, 1–10-veined, narrowly lanceolate to ovate, hyaline or membranous, flexible; florets usually terete, sometimes laterally or dorsally compressed; calluses usually well-developed, rounded or blunt to sharply pointed, often antrorsely strigose; lemmas lanceolate, rectangular, or ovate, membranous to coriaceous or indurate, 3–5-veined, veins inconspicuous, apices entire, bilobed, or bifid, awned, lemma-awn junction usually conspicuous, awns 0.3–30 cm, not branched, usually terminal and centric or eccentric, sometimes subterminal, caducous to persistent, not or once- to twice-geniculate, if geniculate, proximal segment(s) twisted, distal segment straight, flexuous, or curled, not or scarcely twisted; lodicules 2 or 3; anthers 1 or 3, sometimes differing in length within a floret; ovaries glabrous throughout or pubescent distally; styles 2(3–4)-branched. Caryopses ovoid to fusiform, not beaked, pericarp thin; hila linear; embryos less than 1/3 the length of the caryopses. x = 7, 8, 10, 11, 12. The Stipeae includes about 600+ species. It grows in Africa, Australia, South and North America, and Eurasia. In Australia, South America, and Asia, it is often the dominant grass tribe over substantial areas. It is not present in southern India, and is represented by only one native species in southern Africa. Most species grow in arid or seasonally arid, temperate regions. Morphological considerations have led to the Stipeae being placed in three different subfamilies (Poöideae, Bambusoideae, and Arundinoideae) in the past, and even to recognition as a subfamily. Molecular data support its treatment as an early diverging lineage within the Poöideae (Grass Phylogeny Working Group 2001; Schneider et al. 2011) that is more closely related to the Duthieae and Meliceae than the core poöid tribes. Decker (1964) suggested including Ampelodesmos in the Stipeae on the basis of the cross sectional anatomy of its leaf blades. His suggestion is supported, not always strongly, by molecular studies (Grass Phylogeny Working Group 2001; Jacobs et al. 2006; Romaschenko et al. (2010). The usual alternative is to treat Ampelodesmos as the only genus of a closely related, monospecific tribe, the Ampelodesmeae (Conert) Tutin, because it is so distinct from other members of the Stipeae, being, for example, the only member of the tribe with more than 1 floret in its spikelets and rachillas that are prolonged beyond the base of the terminal floret in a spikelet. Romaschenko et al. (2010) suggested that major realignments are needed if the generic treatment of the Stipeae is to reflect the tribe's phylogeny but they have not yet made the necessary combinations to implement their recommendations. The lowest chromosome number known in the Stipeae is 2n = 18 (Prokudin et al. 1977), suggesting that all members of the tribe are ancient polyploids. The wide range of base numbers listed is based on numbers for the various genera. The primary basic chromosome number for the tribe is probably 5 or 6, with higher numbers reflecting ancient euploidy. The hybrid genus ×Achnella is not included in the key; it is treated independently and can be viewed here. SELECTED REFERENCES Barkworth, M.E. 1993. North American Stipeae (Gramineae): Taxonomic changes and other comments. Phytologia 74:1–25; Barkworth, M.E. and J. Everett. 1987. Evolution in the Stipeae: Identification and relationships of its monophyletic taxa. Pp. 251–264 in T.R. Soderstrom, K.W. Hilu, C.S. Campbell, and M.E. Barkworth (eds.). Grass Systematics and Evolution. Smithsonian Institution Press, Washington, D.C., U.S.A. 473 pp.; Decker, H.F. 1964. Affinities of the grass genus Ampelodesmos. Brittonia 16:76–79; Grass Phylogeny Working Group. 2001. Phylogeny and subfamilial classification of the grasses (Poaceae). Ann. Missouri Bot. Gard. 88:373–457; Hsiao, C., S.W.L. Jacobs, N.J. Chatterton and K.H. Asay. 1999. A molecular phylogeny of the grass family (Poaceae) based on the sequences of nuclear ribosomal DNA (ITS). Austral. Syst. Bot. 11:667–688; Jacobs, S.W.L., R. Bayer, J. Everett, M.O. Arriaga, M.E. Barkworth, A. Sabin-Badereau, M.A. Torres, F. Vázquez, and N. Bagnall. 2006. Systematics of the tribe Stipeae using molecular data. Aliso 23:349–361; Jacobs, S.W.L. and J. Everett. 1996. Austrostipa, a new genus, and new names for Australasian species formerly included in Stipa (Gramineae). Telopea 6:579–595; Johnson, B.L. 1945. Cytotaxonomic studies in Oryzopsis. Bot. Gaz. 107:1–32; Prokudin, Y.N., A.G. Vovk, O.A. Petrova, E.D. Ermolenko, and Y.V. Vernichenklo. 1977. Zlaki Ukrainy. Naukava Dumka, Kiev, Russia. 517 pp.; Romaschenko, K., P.M. Peterson, R.J. Soreng, N. Garcia-Jacas, O. Futorna, and A. Susanna. 2008. Molecular phylogenetic analysis of the American Stipeae (Poaceae) resolves Jarava sensu lato polyphyletic: evidence for a new genus, Pappostipa. Journal of the Botanical Research Institute of Texas 2: 165-192; Romaschenko, K., P.M. Peterson, R.J. Soreng, N. Garcia-Jacas, O. Futorna, and A. Susanna. 2010. Phylogenetics of Stipeae (Poaceae: Pooideae) Based on Plastid and Nuclear DNA Sequences. Pp. in O.Seberg, G.Petersen,Barfod & J.I. Davis. Editors) Diversity, phylogeny, and evolution in the monocotyledons. Aarhus University Press, Denmark; Schneider, J, G. Winterfed, M.H. Hofmann, and M. Röser. 2011. Duthieeae, a new tribe of grasses (Poaceae) identified among the early diverging lineages of subfamily Pooideae: molecular phylogenetics, morphological delineation, cytogenetics and biogeography. Systematics and Biodiversity, 9: 27-44. DOI: 10.1080/14772000.2010.544339. Soreng, R.J. and J.I. Davis. 1998. Phylogenetics and character evolution in the grass family (Poaceae): Simultaneous analysis of morphological and chloroplast DNA restriction site character sets. Bot. Rev. (Lancaster) 64:1–85. |