Plants perennial; stoloniferous. Culms 10-40 cm, often decumbent and rooting at the lower nodes. Leaves not aromatic; ligules membranous, ciliate or fimbriate. Inflorescences terminal, solitary rames, spikelets in homomorphic sessile-pedicellate triplets of 2 sessile spikelets and 1 pedicellate spikelet; internodes without a median translucent line; disarticulation in the rames below the sessile spikelets, sometimes also beneath the pedicellate spikelets. Spikelets dorsally compressed, with 1 floret; sessile spikelets bisexual; pedicellate spikelets bisexual, unisexual, or sterile. Glumes equal, oblong, truncate, membranous; lower glumes with the margins incurved over the upper glumes; upper glumes keeled; florets bisexual; lemmas hyaline, bifid almost to the base, awned from the cleft; awns twisted, geniculate; anthers 3. Pedicels not fused to the rame axes. x = 10. Name from the Greek polys, many, and trias, in threes, a reference to the large number and unusual arrangement of the spikelet triads.