Plants perennial. Culms 50-350 cm, decumbent, often rooting from the lower nodes; nodes glabrous; internodes glabrous, filled with spongy aerenchyma. Leaves evenly distributed; ligules membranous. Inflorescences narrow, condensed, cylindrical or spikelike panicles; branches appressed but not fused to the rachises, densely and evenly short ciliate on the ridges. Spikelets dorsally compressed, narrowly lanceolate, with 2 florets. Glumes unequal, membranous, with a definite rachilla internode between the 2 glumes; lower glumes no more than 1/2 as long as the spikelet, 1-3-veined; upper glumes subequal to or longer than the lower lemmas, membranous, not saccate, 3-7-veined; lower florets sterile; lower lemmas similar to the upper glumes; upper florets bisexual, much shorter than the upper glumes and lower lemmas; upper lemmas membranous to leathery, white at maturity, margins clasping the edges of the paleas basally but not distally, apices acute; paleas similar in texture to the lemmas; lodicules 2; anthers 3; styles 2, fused. Caryopses falling free from the lemmas and paleas. x = 10. Name from the Greek hymen, membrane, and achne, chaff, alluding to the membranous upper lemma, an unusual texture for the upper lemma in members of the Paniceae.