Triplasis purpurea is an annual C4 grass (Hilty 2006), 20- 80 cm tall, tufted, stems spreading or reclining, stiff, nodes swollen, white hairy, ligule of short hairs.
Leaves small, stiff, rough above, 0.1-0.2 cm wide, shorter than sheaths, upper leaves much reduced.
Flowers dry, papery, glumes to 0.4 cm, lemmas hairy on veins, apex 2-lobed with short, hairy awn to 1 cm between lobes; terminal inflorescence small 2-8 cm long, sparsely branched, each with a few purple, 2-5 flowered spikelets to 0.8 cm long; blooming Aug.-Oct.
Fruit dry, 1-seeded, grain.
Wetland status: UPL.
Frequency in NYC: Very infrequent. But sometimes locally common.
Habitat: Open, sandy soil, usually coastal.
Notes: All spikelets self pollinating, those of lower inflorescences solitary, enclosed within leaf sheaths; seeds produced in upper inflorescences are smaller and more numerous than those produced in lower inflorescences, the smaller upper seeds are better adapted for wind dispersal; Seeds germinate from late April to early May. Plant sour-tasting (Cheplick and Wickstrom 1999).