Hopia Zuloaga & Morrone

Plants perennial; shortly rhizomatous and long stoloniferous. Culms not not cormous at the base, not branched above the base; nodes swollen, villous, particularly on the stolons. Ligules membranous, papery; blades linear-lanceolate, cross-sections with Kranz anatomy with a single mestome sheath surrounding the vascular bundles and in contact with the metaxylem vessels. Panicles contracted; branches spikelike, appressed, 1-sided, spikelets borne in pairs. Spikelets ellipsoid to obovoid. Lower glumes 3/4-4/5 as long as the spikelets, 5-7-veined; upper glumes subequal to the lower lemmas, 7-11-veined, blunt; lower florets staminate; lower paleas well-developed; upper florets obovoid, indurate, smooth, with microhairs and simple papillae near the base and tip. x = 10.

Hopia is a unispecific genus that extends from the southwestern United States into northern Mexico. Zuloaga et al. (2007) recognized the genus Hopia after based on its unique combination of characteristics: microhairs and papillae on the upper floret, possession of the XYMS- subtype of C4 photosynthesis, chromosome base number of 10, and molecular sequence data. It includes only one species.

1. Hopia obtusa (Kunth) Zuloaga & Morrone
Vine Mesquite

Plants perennial; usually from long slender stolons or shallow rhizomes with swollen, villous nodes. Culms 20-80 cm, often in small clumps, compressed, erect or decumbent, glaucous; lower nodes pubescent; upper nodes glabrous. Lower sheaths ascending, pubescent to pilose; upper sheaths glabrous; ligules 0.2-2 mm, membranous, truncate, irregularly denticulate; blades 3-26 cm long, 2-7 mm wide, ascending, firm, glaucous, sparsely pilose near the base, often scabrous on the margins, involute towards the apices. Panicles 5-15 cm long, 0.8-1.5 cm wide; branches 2-6, spikelike, erect, puberulent, 3-angled; ultimate branchlets 1-sided; pedicels paired, congested, shorter pedicels 0.1-1 mm, longer pedicels 1.5-2.5 mm. Spikelets 2.8-4.4 mm, ellipsoid, terete to slightly laterally compressed, glabrous, obtuse. Lower glumes about 3/4 as long as the spikelets, 5- or 7-veined; upper glumes and lower lemmas equaling the spikelets, 5-9-veined; lower florets staminate; lower paleas 2.5-3.5 mm; upper florets puberulent at the bases and apices. 2n = 20, 36, 40.

Hopia obtusa grows in seasonally wet sand or gravel, especially on stream banks, ditches, roadsides, wet pastures, and rangeland. Its range extends from the southwestern United States to central Mexico. Flowering is from May through October.