Chorisporsa tenella, commonly known as Blue Mustard, is an annual herb 1 to 5dm tall. The flowers are arranged in loosely packed racemes of slender purple flowers 7 to 10mm long. The corolla is composed of 4 petals forming the chracteristic cross of the Brassicaceae family. The stamens are arranged in a didynymous fashion with 2 long and 4 short, characteristic of the family as well. Leaves are elliptic to oblong, all but the few top ones being petiolate and are 3 to 8cm long. The margins are dentate. The fruit produced is a silique that is constricted between each seed, that will rupture crosswise but will not dehisce. The upper portion of the silique is sterile and forms a long slender beak, approximately 7 to 20mm long. The fruit will produce several seeds.
C. tenella is a weedy Eurasian species that is widely established in dry areas, rarely found west of the Cascade mountain range.
The above photo was taken along a stream in Caldwell, Idaho in April 2007.
Hitchcock, C.L. and A. Cronquist (1994) Flora of the Pacific Northwest, University of Washington Press, Seattle and London.