Bromus madritensis is a winter annual grass, growing solitary or tufted, with erect or ascending
culms growing high. The leaf sheaths are downy or slightly hairy. The grass lacks
auricles and the glabrous
ligules are long. Its flat leaf blades are either glabrous or slightly hairy, and measure long and wide. The erect and ellipsoid
panicles are long and wide, with short branches that ascend and slightly spread. The branches never droop and bear one or two
spikelets each. The spikelets are long, longer than the panicle branches, and bear seven to eleven
florets. The spikelets vary in color from green to distinctly purplish-red. The lightly hairy
glumes taper at their ends and have translucent margins. The lower glumes are one-nerved and long, and the upper glumes are three-nerved and long. The glabrous and slightly rough
lemmas are long. The lemmas are hairier towards their edges and have five to seven veins. The
awns are about the same length, long, and curve slightly. The
anthers are long. The
caryopses are as long as . The grass emerges in early winter and remains dormant until spring when heavy rainfall and higher temperatures stimulate growth. Plants flower from this period typically until May when
water stress inhibits the grass. Populations grow during periods of heavy rainfall and populations can be wiped out during extended periods of drought. The grass alters soil conditions and the
competition brought about by the grass both negatively affect native plant populations, and the highly flammable nature of the grass produces wildfires in North American communities where fire was previously rare. Dry
florets of the weed entangle themselves in animal hair and can tear at the
digestive tracts of foraging livestock. ==Habitat and distribution==