Plants annual; tufted. Culms 20-100 cm, not swollen at the base. Ligules 3-5 mm, truncate to acute; blades 5-10(15) cm long, 2-5 mm wide. Panicles 3-9 cm long, about 2 cm wide, dense, obovoid to clavate, tapering at the base, rounded to truncate at the top; branches with groups of 5-6 usually staminate, rarely sterile spikelets clustered around a terminal pistillate or bisexual spikelet, the spikelets homomorphic; pedicels hispid; disarticulation beneath the spikelet cluster. Spikelets heterogamous, some staminate or sterile, others bisexual or pistillate; florets 3, the lowest 2 florets sterile, highly reduced, the terminal floret staminate, pistillate, or bisexual (rarely sterile). Glumes of staminate or sterile spikelets usually narrowly winged and to 9 mm long and clavate, those of the spikelets at the base of the panicles reduced to knobs of tissue terminating the pedicels; glumes of pistillate or bisexual spikelets 5-8 mm long, about 1 mm wide, keeled, keels winged, wings 0.2-0.4 mm wide, terminating below the apices and forming a single, prominent tooth, lateral veins conspicuous, apices acuminate to awned, awns about 0.5 mm; sterile florets of all spikelets 0.2-0.4 mm, knoblike projections on the calluses of the terminal florets, often with 1-2 hairs; terminal florets of all spikelets 2.5-3.5 mm long, 0.8-1.5 mm wide, indurate, shiny, glabrous or with a few short hairs near the tip; anthers 1.5-2.5 mm. 2n = 14.
Phalaris paradoxa is native to the Mediterranean region; it is now found throughout the world, primarily in harbor areas and near old ballast dumps. It is an established weed in parts of Arizona and California. Within an inflorescence, the most reduced sterile spikelets are located near the base, and the most nearly normal spikelets are near the top.