Plants annual. Culms 15-65 cm, erect or geniculate, branching from
the lower nodes; nodes glabrous or hispid. Sheaths glabrous or with
papillose-based hairs, margins ciliate distally; ligules 1-1.6 mm; blades
5-15 cm long, 5-12 mm wide, glabrous. Panicles 6-20 cm long, 2-5 cm wide,
ovoid, with 6-12 spikelike primary branches in more than 2 ranks; primary branches
3-7 cm, divergent, axes about 0.4 mm wide, triquetrous, densely pubescent
with papillose-based hairs; secondary branches short, divergent; pedicels
shorter than the spikelets, with papillose-based hairs. Spikelets 3.2-4
mm long, 1.2-1.6 mm wide, mostly paired, in 2 rows, appressed to the branches.
Glumes scarcely separate, rachilla internodes short, not pronounced; lower
glumes 1.5-2 mm, to 1/2 as long as the spikelets, glabrous, 5-veined, sometimes
with evident cross venation near the apices; upper glumes 2.5-3.2 mm, glabrous
or shortly hirsute, 7-veined, with evident cross venation distally; lower florets staminate
or sterile; lower lemmas 2.5-3.2 mm, glabrous or shortly hirsute, 5-veined,
about as long as the spikelet; lower paleas present; upper lemmas
2.8-3 mm long, 1.2-1.6 mm wide, acute, beaked or mucronate; anthers 0.8-1
mm. Caryopses 1.5-2 mm; hila punctiform. 2n = 36.
Urochloa arizonica is native to the southwestern United States and northern Mexico, but has been introduced and appears to be established in the southeastern United States. It grows in open, dry areas with rocky or sandy soils.
FNA 2003, Gould 1988
Common Name: Arizona signalgrass Duration: Annual Nativity: Native Lifeform: Graminoid General: Annual grass, 15-60 cm tall; stems erect or geniculate, much-branched at the lower nodes, glabrous or sparsely hispid at the nodes and below the panicle. Vegetative: Sheaths glabrous to papillose-hispid, loose; blades 5-15 mm broad, glabrous or scabrous, ciliate on margins at least near the base; ligules 1-1.5 mm. Inflorescence: Panicle 7-20 cm long with appressed or erect-spreading hairs, branches scabrous; pedicels 1-3 mm long, paired, appressed, glabrous or pubescent; spikelets mostly 3-4 mm long, 2-flowered, the first floret reduced to a sterile lemma and the second floret fertile; first glume half or slightly less as long as the spikelet; second glume and sterile lemma puberulent or glabrous, abruptly pointed at apex; fertile lemma indurate, reticulate or finely rugose, abruptly short-beaked or cuspidate, 2-3 mm long. Ecology: Found on sandy ground, rocky slopes, and canyon bottoms from 1,000-5,500 ft (457-1676 m); flowers June-October. Distribution: s CA, AZ, s NM, s TX; south to s MEX. Notes: Formerly recognized as Panicum, this annual grass has the hard, single-seeded spikelets that define that group. Distinguish from annuals Panicum capillare and P. hirticaule by the fertile lemmas which are not smooth and shiny but have wrinkles or reticulation. To distinguish from from B. fusca look for the presence of enlarged bases of hairs on inflorescence branches. Also distinguished by having broad, ciliate flag leaves. Ethnobotany: Unknown Etymology: Brachiaria from the Latin brachium, arm, alluding to the arm-like racemes (more obvious in other species of the genus); arizonica refers to Arizona. Synonyms: Brachiaria arizonica, Panicum arizonicum, Urochloa arizonica Editor: SBuckley 2010, FSCoburn 2015, AHazelton 2015