Plants perennial; cespitose, with a dense, hard, knotty base, rhizomatous, rhizomes 2-3 mm thick, with pale cataphylls; internodes 4-5 mm. Culms (40) 60-80 cm, erect, straight, unbranched. Sheaths strongly striate; ligules 0.5-1 mm, of hairs; blades mostly basal, short and firm, 2-3 mm wide, bases with papillose-based hairs on the margins. Panicles 10-15 cm, usually with 7-12 branches; branches (15)20-30 mm, deciduous, with 8-11 spikelets, apices entire; disarticulation at the base of the branches. Spikelets appressed, all alike, with 2 florets, lowest floret bisexual, upper florets pistillate, bisexual, or staminate. Glumes acuminate, glabrous; lower glumes about 4 mm; upper glumes 5-6 mm; lowest lemmas 7-8 mm, smooth, often shortly trilobed, 3-awned, awns extending from the lobes, central awns 2-3 mm, not flanked by membranous lobes, lateral awns about 1 mm; lower paleas 6-7 mm, unawned, sometimes mucronate; upper lemmas 9-10 mm, central awns 6-8 mm, lateral awns 5-6 mm; upper paleas similar to the lower paleas. Caryopses 4-5 mm long, 0.75-1 mm wide. 2n = 60.
Bouteloua radicosa grows on dry, rocky slopes at 1000-3000 m, from Arizona and southern New Mexico to southern Mexico. It has also become established in Maine, growing in disturbed habtiats, but is not common there.
Bouteloua radicosa frequently grows with B. repens at lower elevations, but extends higher than that species. Like B. repens, B. radicosa exhibits great variation in spikelet and inflorescence characters. Gould (1979) suggested that some of the variation in B. radicosa was due to hybridization with B. repens in the Flora area and B. williamsii Swallen in southern Mexico. This hypothesis has not been tested.
Common Name: purple grama
Duration: Perennial
Nativity: Native
Lifeform: Graminoid
General: Cespitose perennials with dense, hard, knotty base, with rhizomes 2-3 mm thick, rhizome covered by firm, coarse, flattened, light-colored leaf sheaths (cataphylls).
Vegetative: Erect, straight and unbranched stems 40-80 cm, strongly striate sheaths, ligules 0.5-1 mm of hairs; blades mostly basal, short and firm, 2-3 mm wide, bases with papillose-based hairs on the margins.
Inflorescence: Panicles 10-15 cm, usually with 7-12 deciduous branches; branches 20-30 mm bearing 8-11 spikelets with entire apices; disarticulation at the base of branches; spikelets appressed, all alike, with 2 florets, lowest bisexual, upper pistillate, bisexual, or staminate; glumes acuminate, glabrous, lower about 4 mm, upper 5-6 mm, lowest lemmas 7-8 mm, smooth, often shortly trilobed, 3-awned with awns extending from lobes, central awns 2-3 mm, not flanked by membranous lobes, lateral awns about 1 mm; flowers August-October.
Ecology: Found on dry rocky slopes; 3,500-7,000 ft (1067-2134 m).
Distribution: s AZ, s NM; south to s MEX.
Notes: This species is a part of a group of Boutelouas very similar in appearance being perennials, often caespitose, with short, deciduous inflorescence branches (sometimes appearing as clusters of spikelets) on both sides of the axis which completely fall off, leaving a small nodule behind. B. radicosa is distinguished from B. repens, B. chondrosoides and B. eludens by its hard, knotty, rhizomotous bases. None of these other species have this character.
Ethnobotany: Unknown, but other species in the genus have uses.
Etymology: Bouteloua named for brothers Claudio (1774-1842) and Esteban (1776-1813) Boutelou Agraz, Spanish botanists and horticulturalists; the origin of radicosa is uncertain, probably referring to its roots.
Synonyms: Atheropogon radicosus
Editor: SBuckley 2010, FSCoburn 2014
