Plants perennial; cespitose, with innovations, without rhizomes, not
glandular. Culms 30-110 cm, erect, glabrous below the nodes. Sheaths
glabrous or pilose, hairs to 5 mm; ligules 0.1-0.2 mm; blades
8-22 mm long, (1)2-4(5) mm wide, flat to folded, glabrous abaxially, scabridulous
adaxially. Panicles 18-70 cm long, 3-25 cm wide, diffuse, ovate; primary
branches 4-20 cm, appressed or diverging 10-70° from the rachises, naked
basally; pulvini glabrous; pedicels 2.4-11 mm, divergent. Spikelets
1.3-2 mm long, 0.8-1.8 mm wide, ovate to lanceolate, plumbeous, with 1-3 florets;
disarticulation acropetal, in the rachilla below the florets, glumes
deciduous; rachilla prolonged above the terminal floret. Glumes
lanceolate to ovate, membranous; lower glumes 0.8-1 mm; upper glumes
1.1-1.4 mm; lemmas 0.8-1.2 mm, ovate, membranous, plumbeous, keels and
lateral veins inconspicuous, apices obtuse; paleas 0.8-1.2 mm, membranous,
bases not projecting beyond the lemmas, apices obtuse; anthers 3, 0.3-0.5
mm, purplish. Caryopses 0.4-0.5 mm, ovoid, reticulate, reddish-brown.
2n = 36 (Davidse, pers. comm.).
Eragrostis airoides is a South American species that, in the Flora
region, is known only from roadsides and disturbed sites in Brazos County, Texas.
It is an enigmatic species, often treated as Sporobolus brasiliensis
(Raddi) Hack., which it resembles in its
chromosome base number of x = 9 and caryopsis morphology, but its frequent
possession of spikelets with more than 1 floret and its mode of spikelet disarticulation
argue for its retention in Eragrostis.