10. STIPEAE Dumort.
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; disarticulation above 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: evidene for a new genus, Pappostipa.
Journal of the Botanical Research Institute of Texas 2: 165-192.
Journal of the Botanical Research Institute of Texas 2: 165-192;
Journal of the Botanical Research Institute of Texas 2: 165-192.
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. WINTERFELD, M.H. HOFFMANN, 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: 10.1080/14772000.2010.544339Soreng, 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.
|1.||Spikelets with 2-6 florets||Ampelodesmos|
|Spikelets with only 1 floret||2|
|2.||Paleas longitudinally grooved; lemma margins involute, fitting into the palea groove; lemma apices neither lobed nor bifid||Piptochaetium|
|Paleas flat for all or most of their length, sometimes pinched at the tip; lemma margins flat; lemma apices often lobed, sometimes bifid, sometimes not lobed||3|
|3.||Prophylls exceeding the leaf sheaths; lemma apices bifid; plants occasionally cultivated as ornamentals||4|
|Prophylls shorter than the leaf sheaths; lemma apices lobed, unlobed, or bifid; plants native, established introductions, or ornamentals||5|
|4.||Panicles contracted; lemma awns once-geniculate||Macrochloa|
|Panicles open; lemma awns twice-geniculate||Celtica|
|5.||Flag leaves highly reduced, no more than 12 mm long; basal leaves overwintering, their blades resupinate||Oryzopsis|
|Flag leaf blades well developed, more than 12 mm long; basal leaves not overwintering, their blades not resupinate||6|
|6.||Plants with multiple stiff branches from the upper nodes; pedicels sometimes plumose; plants known in cultivation in North America||Austrostipa|
|Plants either not branching from the upper nodes or the branches few and flexuous; pedicels not plumose; plants native, established, or cultivated in North America||7|
|7.||Leaf blades with sharp, stiff tips; caryopses obovoid, often with 3 smooth ribs at maturity; cleistogenes often present||Amelichloa|
|Leaf blades acute or acuminate, neither sharp nor stiff; caryopses fusiform, oblong, or ovoidm, without ribs; cleistogenes sometimes present||8|
|8.||Lemma margins strongly overlapping their whole length at maturity; lemma bodies usually rought throughout, apices not loped; paleas 1/4-1/2 the length of the lemmas, without veins, glabrous||Nassella|
|Lemma margins usually not or only slightly overlapping for some or all their length at maturity, strongly overlapping in some species with smooth lemmas; lemma bodies usually smooth on thelower portion, apices often 1-2 lobed, sometimes bifid; paleas from 1/3 as long as to slightly longer than the lemmas, 2-veined, at least on the lower portion, usually with hairs, glabrous in species with glabrous lemmas||9|
|9.||Calluses 1.5-6 mm long, sharply pointed; plants perennial and the lemma awns 65-500 mm long or plants annual and the lemma awns 50-100 mm long; panicle branches straight||10|
|Calluses 0.1-2 mm long, blunt to sharply pointed; plants perennial; awns 1-70 mm long; panicle branches straight or flexuous||12|
|10.||Lower ligules densely hairy, upper ligulesinconspicuously hairy, sometimes glabrous; lowest segment of awn pilose; plants perennial||Pappostipa|
|Ligules glabrous or inconspicuously hairy, lower and upper ligules alike in this respect; plants annual or perennial||11|
|11.||Plants perennial; florets 7-25 mm long; awns scabrous or pilose on the first two segments, the terminal segment scabrous or pilose with hairs 1-3 mm long||Hesperostipa|
|Plants annual, with florets 4-7 mm long and lemma awns scabridulous on the terminal segment or perennial with florets 18-27 mm long and lemma awns pilose on the terminal segment||Stipa|
|12.||Florets usually dorsally compressed at maturity, sometimes terete; paleas as long as or longer than the lemmas and similar in texture and hairiness; lemma margins not overlapping at maturity||Piptatherum|
|Florets terete or laterally compressed at maturity; paleas often shorter and less hairy than the lemmas, sometimes as long as the lemmas and similar in texture and hairiness; lemma margins usually overlapping for most or all of their length at maturity||13|
|13||Glumes without evident venation; glume tips rounded to acute; plants subalpine to alpine, sometimes growing in bogs||Ptilagrostis|
|Glumes with 1-3(5) evident veins; glume tips acute to attenuate; plants from near sea level to alpine, not growing in bogs||14|
|14.||Lemma bodies glabrous, with evenly distributed hairs of similar length, or with longer hairs around the base of the awn; basal segment of the awn scabrous or with hairs up to 2 mm long||Achnatherum|
|Lemma bodies with hairs to 1 mm long over most of the length and strongly divergent hairs 3-8 mm long on the distal 1/4 or the basal segment of the awn with hairs 3-8 mm long||Jarava|