Plants perennial, usually cespitose, occasionally rhizomatous. Culms 30-125 cn takk, 1-3 mm in diameter, erect, terete to flattened, glabrous; nodes 2-5; lowest internodes not swollen. Sheaths smooth or scabridulous, ribbed; ligules 10-20 mm long, acute to acuminate; blades 10-30 cm long, 1.5-3.5 mm wide, flat or involute, smooth to scabrous, abaxial surfaces scabridulous, adaxial surfaces deeply ribbed, scabrous. Terminal panicles 15-40 cm long, erect, sparse, the lower portion sometimes partially enclosed in the uppermost sheath; branches usually 7-15 cm long, ascending or appressed, often flexuous; pedicels usually 10-20 mm long. Spikelets 10-16 mm long, with 4-6 florets. Glumes unequal to subequal, green or, sometimes, purplish in the center, with hyaline margins; lower glumes 2.5-3.5 mm long, 305-veined; upper glumes 3-6.5 mm long, 3-5-veined; lemmas 5-7.2 mm long, 5-7-veined, scabrous, tips not appearing constricted, usually 4-toothed, 2 lateral teeth smaller that the central pair, awned, awns inserted on the lower 2/5-3/5 of the lemma, geniculate and twisted; paleas 3/4 as long as to subequal to the lemmas, papillose; anthers of cleistogamous florets 0.3-1.4 mm long, those of the chasmogamous forets 2.2-3 mm long.
Amphibromus nervosus is the most widespread species of the genus, growing in swamps and on floodplains riverbanks of both southwestern and southeastern Australiia. It was collected in 1990 from a vernal pool in Sacramento County, California. Seeds had been found earlier as a contaminant of Trifolium subterranean. The discovery of living plants are of particular concern because of their ability to invade and survive in vernal pools.