Achnatherum robustum |
Poaceae tribe Stipeae |
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sleepy grass |
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Habit | Plants cespitose, not rhizomatous. | Plants usually perennial; usually tightly to loosely cespitose, sometimes rhizomatous. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Culms | 100-230 cm tall, 2-4.5 mm thick, mostly glabrous, often pubescent below the nodes, the pubescence antrorse or retrorse; nodes 4-5. |
annual or perennial, not woody, branches 1 to many at the upper nodes. |
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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. |
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Panicles | 15-30 cm long, 0.8-3.5 cm wide; branches straight, appressed to ascending, lower branches 3-9 cm. |
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Inflorescences | usually terminal panicles, occasionally reduced to racemes in depauperate plants, sometimes 2-3 panicles developing from the highest cauline node. |
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Spikelets | appressed to the branches. |
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. |
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Glumes | subequal, 9-11.5 mm long, 1-1.4 mm wide; florets 5.9-8.5 mm long, 0.9-1.2 mm thick, fusiform, terete; calluses 0.3-1 mm, blunt; lemmas evenly hairy, hairs at midlength 0.3-0.8 mm, apical hairs to 1.5 mm; awns 20-32 mm, persistent, twice-geniculate, scabridulous to scabrous, scabrules to about 0.1 mm, longest on the middle segment, terminal segment straight; paleas 3.7-5.6 mm, 2/3 - 3/4 as long as the lemmas, hairy, hairs about 0.5 mm, not exceeding the apices, veins terminating below the apices, apices rounded; anthers 4-5 mm, dehiscent, penicillate. |
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. |
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Caryopses | 5-6 mm. |
ovoid to fusiform, not beaked, pericarp thin; hila linear; embryos less than 1/3 the length of the caryopses. |
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Basal | sheaths mostly glabrous, margins usually ciliate distaily; collars hairy, those of the flag leaves densely hairy, hairs 0.5-2 mm, sides glabrous; basal ligules 1-2 mm; upper ligules to 4 mm, truncate, rounded, or obtuse, glabrous; blades 6-10 mm wide, glabrous, abaxial surfaces smooth, adaxial surfaces prominently ribbed, ribs scabrous. |
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x | = 7, 8, 10, 11, 12. |
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2n | = 64. |
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Achnatherum robustum |
Poaceae tribe Stipeae |
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Distribution |
AZ; CO; KS; NE; NM; SD; TX; WY
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Discussion | Achnatherum robustum grows on dry plains and hills, in open woods and forest clearings, and along roadsides, from Wyoming through Colorado to Arizona, New Mexico, and northern Mexico. Records from Kansas represent recent introductions; it is not clear whether the species has persisted there. Achnatherum robustum is sometimes confused with A. nelsonii subsp. dorei and Nassella viridula; it differs from both in the densely hairy collars of its flag leaves. Although not widely available, it has potential as an ornamental grass, particularly in arid regions with cold winters. The English-language name refers to the effect some samples, particularly those from the Sacramento and Sierra Blanca mountains, New Mexico, have on livestock, especially horses and cattle. "Mildly poisoned animals are dejected, inactive, and withdrawn; severely poisoned animals lie on their sides in a profound slumber" (Cheeke and Shull 1985). The active ingredient is diacetone alcohol (Epstein et al 1964). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
The tribe Stipeae includes about 15 genera and approximately 500 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 (Pooideae, 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 Pooideae (Soreng and Davis 1998; Grass Phylogeny Working Group 2001) that is more closely related to the Meliceae than the core pooid 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 (Soreng and Davis 1998; Grass Phylogeny Working Group 2001; Jacobs et al. 2006). 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. 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. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 24, p. 129. | FNA vol. 24, p. 109. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Parent taxa | Poaceae > subfam. Pooideae > tribe Stipeae > Achnatherum | Poaceae > subfam. Pooideae | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Synonyms | Stipa vaseyi, Stipa robusta | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Name authority | (Vasey) Barkworth | Dumort. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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