Plants perennial; cespitose, rhizomatous, rhizomes short, thin. Culms clumped or solitary, often with hard, cormlike bases, slightly compressed, erect or geniculate at the lower nodes. Sheaths shorter than the internodes, keeled, often pilose, hairs papillose-based near the throat; ligules membranous-based, ciliate; blades (6)20-75 cm long, 1.5–15 mm wide, flat, adaxial surfaces scabrous. Panicles pyramidal, open, bearing 4–40 branches, basal node with 1 branch; primary branches to 30 cm, with 3–6 orders of branching, straight or flexible, ascending to reflexed; pedicels scabridulous, divergent. Spikelets 2.5-4.2(5.5) mm long, ellipsoid or lanceoloid, purplish or greenish, glabrous, acute or obtuse. Lower glumes 1–3.7 mm, about 2/3 as long as the upper glumes, 3-5-veined; upper glumes slightly shorter to subequal to the lower lemmas, glabrous, 5–7-veined; lower florets sterile or staminate; lower lemmas 2.9–3.3 mm, glabrous, 5-veined, acute; lower paleas 3-4 mm, hyaline; upper florets 2.1–5 mm long, exceeding the upper glumes, margins embracing the the lower lemmas, dull, pale, finely transversely rugose, apices acute, puberulent; anthers about 2 mm, yellow-brown; stigmas pale purple, plumose. Caryopses oblong, compressed, embryos about 1/3 the length of the caryopses. x= 9
Zuloagaea is a unispecific genus that is native to western North America. It used be included in Panicum, but molecular phylogenetic studies consistently place it in the bristle clade of the Paniceae (Gómez-Martín and Culham 2000; Giussani et al. 2001; Aliscioni et al. 2003; Bess et al. 2005). Other genera in this clade include Cenchrus, Pennisetum, and Setaria. Its membership in the clade is puzzling, for it lacks any evidence of bristle development. Bess et al. (2005) concluded that removing it from Panicum was essential if that genus is to be monophyletic. Including it in a genus with evident bristles seemed inappropriate so they placed it in a genus of its own. They noted that is recognizable by its "open, loosely-flowered pyramidal panicle with small spikelets that are purple in color if the plant is growing in the sun, or green in color if it is growing in the shade". Its distinctive vegetative characters include the thickened, often cormous, culm bases, elongate blades, and rather short, often pilose sheaths.
1. Zuloagaea bulbosa ( Kunth) Bess
Culms 20-200 cm tall, 1-8 mm thick, erect or geniculate at the lower nodes; nodes glabrous or pilose; internodes glabrous. Sheaths shorter than the internodes, keeled, glabrous or pilose, hairs near the throat papillose-based; ligules with a 0.1-2 mm membranous base and 0.10–3 mm ciliate fringe; blades (6)20-75 cm long, 1.5–15 mm wide. Panicles 9-75 cm long, width to about 2/3 length; branches straight or flexible, strongly ascending to reflexed; pedicels 0.2-5 mm. Spikelets 2.5-5.5 mm long, 1-2 mm wide. Lower glumes 1.2-3.5 mm, 1/2-4/5 as long as the spikelets, 3-5-veined; upper glumes 1.4–4 mm; lower florets sterile or staminate; lower lemmas 2.9–3.3 mm; upper florets 2.1–5 mm long, 1-1.5 mm wide, lemma apices puberulent. 2n = 36, 54, 70, 72.
Zuloagaea bulbosa grows in roadside ditches, on gravelly river banks and moist mountain slopes, often in ponderosa pine and oak woodlands, from southern Nevada and Arizona to western Texas and central Mexico. It is considered an important forage grass and is sometimes cut for hay but is not known to be cultivated. Flowering is from July to mid-October.
In the past, three species have been recognized within Panicum sect. Bulbosum. Bess et al. (2006) demonstrated that the variation is continuous and highly influenced by environment. Their recommendation, that Hopia be treated as a unispecific genus, is followed here. Plants growing in sunlight tend to have purple spikelets, those growing in the shade tend to have green spikelets.