Plants annual or perennial; synoecious; habit various, cespitose, stoloniferous, or rhizomatous. Culms 1-80 cm. Leaves usually mostly basal; sheaths open; ligules of hairs, membranous, or membranous and ciliate. Inflorescences terminal, panicles of 1-80 solitary, spikelike branches, exceeding the upper leaves; branches 4-50(75) mm, not woody, 1-sided, usually racemose on elongate rachises, sometimes digitate or subdigitate, with 1-130+ sessile to subsessile spikelets in 2 rows, axes terminating in a spikelet or extending beyond the base of the distal spikelet. Spikelets closely imbricate, appressed to pectinate, laterally compressed or terete, with 1-2(3) florets, lowest floret in each spikelet bisexual, distal florets staminate or sterile; disarticulation at the base of the branches or above the glumes. Glumes unequal or subequal, 1 or both glumes equaled or exceeded by the distal floret, 1-veined, acute or acuminate, sometimes shortly awned; lower glumes usually shorter than the lowest floret; lemmas of lowest florets entire, bilobed, trilobed, or 4-lobed, 3-veined, veins usually extended into 3 short awns; paleas of lowest florets 2-veined, veins sometimes excurrent; distal floret(s) staminate or sterile, varying from similar to the lowest floret in shape, size, and venation to sterile and reduced to an awn column with well-developed awns or to a flabellate scale, x = 10.
Distribution
Conn., N.J., N.Y., W.Va., Mich., Alta., B.C., Man., Ont., Sask., D.C, Wis., Ariz., N.Mex., Pacific Islands (Hawaii), Idaho, Oreg., Fla., Wyo., Tex., La., Md., Maine, Miss., S.C., N.C., Nebr., Tenn., Pa., Mass., Ala., Ga., Ill., Ind., Ky., Minn., N.Dak., Ohio, S.Dak., Utah, Mont., Va., Colo., Calif., Puerto Rico, Virgin Islands, Kans., Okla., Ark., Iowa, Nev., Wash., Mo.
Discussion
Bouteloua, a genus of the Western Hemisphere with its center of diversity in Mexico, has about 40 species; all 19 species treated here are native to the Flora region. Several of its taxa are important forage grasses, and some are important constituents of the native North American grasslands. Two that are particularly important in North America are Bouteloua curtipendula and B. gracilis. These were major constituents of the shortgrass prairie that once covered the drier portions of the Great Plains. Both are excellent forage species. Irrigation has converted much of the area they once occupided to agricultural use, but large areas of Bouteloua grasslands remain.
Based on molecular data and morphological similarities in the non-pistillate characters, Columbus (1999) recommended expanding Bouteloua to include Buchloë, Opizia, and Cathestecum, plus some other small genera not known from the Flora region. The traditional treatment is adopted here, pending corroboration from a wider range of data, both molecular and morphological.
Selected References
Lower Taxa
Key
| 1 | Panicle branches deciduous, disarticulation occurring at their bases; spikelets usually 1-15 per branch, usually appressed rather than pectinate (subg. Bouteloua). | > 2 |
| 2 | All or most panicle branches with 1 spikelet | Bouteloua uniflora |
| 2 | All or most panicle branches with 2-15 spikelets. | > 3 |
| 3 | First (proximal) spikelet on each branch with 1 floret, the remaining spikelets with 2 florets; plants annual; panicles with 1-15 branches | Bouteloua aristidoides |
| 3 | Spikelets all alike or with 2 or more florets; plants annual or perennial; panicles with 1-80 branches. | > 4 |
| 4 | Central awns of lemmas flanked by 2 membranous lobes at maturity, the lobes 0.5-1.5 mm. | > 5 |
| 5 | Upper glumes bilobed, awned, the awns arising from between the teeth; inflorescence branch axes with deeply bi- or trifurcate apices; second florets sterile, rudimentary | Bouteloua rigidiseta |
| 5 | Upper glumes acute, unawned or awn-tipped; inflorescence branch axes with apices entire; second florets usually staminate. | > 6 |
| 6 | Base of plants dense, hard and knotty; culms straight, unbranched; panicle branches (15)20-30 mm long; plants rhizomatous | Bouteloua radicosa |
| 6 | Base of plants usually not dense, hard, or knotty; culms straight or geniculate, branching; panicle branches 10-20 mm long; plants not rhizomatous | Bouteloua repens |
| 4 | Central awns of lemmas, if present, not flanked by membranous lobes or the lobes less than 0.3 mm long. | > 5 |
| 7 | Upper glumes with hairs, at least over the midveins. | > 8 |
| 8 | Upper glumes with hairs only over the veins | Bouteloua repens |
| 8 | Upper glumes with hairs over the veins and elsewhere. | > 9 |
| 9 | Panicles 6-10 cm long; branches with 2-6 spikelets | Bouteloua eludens |
| 9 | Panicles 2.5-6 cm long; branches with 8-12 spikelets | Bouteloua chondrosoides |
| 7 | Upper glumes glabrous, sometimes scabrous. | > 8 |
| 10 | Second florets sterile, usually rudimentary, usually without paleas; central awns rarely to 7 mm long; panicles with 9-80 branches. | > 11 |
| 11 | At least some leaf blades more than 2.5 mm wide, flat or folded when dry; ligules 0.3-0.5 mm long; anthers yellow, orange, red, or purple | Bouteloua curtipendula |
| 11 | Leaf blades 1-1.5(2.5) mm wide, involute when dry; ligules 1-1.5 mm long; anthers dark purple | Bouteloua warnockii |
| 10 | Second florets bisexual, pistillate or staminate, with well-developed paleas; central awns 4-10 mm long; panicles with 2-17 branches. | > 11 |
| 12 | Base of plants dense, hard and knotty; culms straight, unbranched; panicle branches (15)20-30 mm long; plants rhizomatous | Bouteloua radicosa |
| 12 | Base of plants usually not dense, hard, or knotty; culms straight or geniculate, branching; panicle branches 10-20 mm long; plants not rhizomatous | Bouteloua repens |
| 1 | Panicle branches persistent; disarticulation above the glumes; spikelets 6-130 or more per branch, pectinate (subg. Chondrosum). | > 2 |
| 13 | Upper glumes of at least some spikelets with papillose-based hairs. | > 14 |
| 14 | Panicle branches extending beyond the base of the terminal spikelets | Bouteloua hirsuta |
| 14 | Panicle branches terminating in a spikelet. | > 15 |
| 15 | Plants tufted annuals or short-lived stoloniferous perennials; panicle branches 4-8, the axes with papillose-based hairs; lowest lemmas 3-4 mm long | Bouteloua parryi |
| 15 | Plants perennial, often shortly rhizomatous; panicle branches 1-3(6), the axes scabrous, never with papillose-based hairs; lowest lemmas 3.5-6 mm long | Bouteloua gracilis |
| 13 | Upper glumes glabrous, scabrous, or hairy, but the hairs not papillose-based. | > 14 |
| 16 | Lower cauline internodes woolly-pubescent | Bouteloua eriopoda |
| 16 | Lower cauline internodes glabrous or mostly so, sometimes pubescent immediately below the nodes. | > 17 |
| 17 | Central awns of lemmas not flanked by membranous lobes | Bouteloua trifida |
| 17 | Central awns of lemmas flanked by 2 membranous lobes. | > 18 |
| 18 | Lowest paleas in the spikelets awned, awns 1-2 mm long; panicles with 2-20 branches. | > 19 |
| 19 | Lowest lemmas glabrous, with awns 3-4 mm long; panicle branches with 6-20 spikelets; plants perennial | Bouteloua kayi |
| 19 | Lowest lemmas densely pilose, with awns 0.5-3 mm long; panicle branches with 20-50 spikelets; plants annual or short-lived perennials | Bouteloua barbata |
| 18 | Lowest paleas in the spikelets unawned, but the veins sometimes excurrent for less than 1 mm; panicles with 1-6 branches. | > 19 |
| 20 | Plants annual | Bouteloua simplex |
| 20 | Plants perennial. | > 21 |
| 21 | Culms usually with 2-3 nodes, not woody at the base; caryopses 2.5-3 mm long; lower paleas shallowly bilobed, the veins sometimes excurrent | Bouteloua gracilis |
| 21 | Culms usually with 4-5 nodes, somewhat woody at the base; caryopses 1-1.2 mm long; lower paleas acute to acuminate, the veins not excurrent. | > 22 |
| 22 | Lower culm internodes with a thick, white, chalky bloom distally; panicle branches stramineous, mostly appressed, usually straight to slightly arcuate; plants rhizomatous, growing on gypsum soils | Bouteloua breviseta |
| 22 | Lower culm internodes without a conspicuous bloom; panicle branches dark, mostly ascending to widely divergent, usually becoming arcuate; plants not rhizomatous, growing on limestone soils | Bouteloua ramosa |