Trichostema setaceum is an annual herb to 30 cm, stems sparsely branched, finely hairy.
Leaves opposite, linear, 1-veined, to 0.5 cm wide.
Flowers blue, irregular, to 1 cm long, 5-lobed, lowest lobe longer than other 4, stamens blue, much longer that petal lobes, filaments to 1.5 cm, arching upward and curled back, calyx tubular, longest teeth are lowest, to 0.5 cm long, becoming 0.9 in fruit; Aug-Sept.
Fruit dry nutlets to 0.3 cm.
Wetland status: UPL.
Frequency in NYC: Very infrequent.
Habitat: Dry soil.