Tansy Mustard
Descurainia pinnata
Photographed at Vulture Peak, Maricopa Co., Arizona, USA. March 2008.
LEAVES: Leaves are thrice - or more - pinnately divided. Ultimate segments are almost minute.
This photo from a plant at South Mountain in Phoenix. Resting on the leaf is a very small fly which could be a kind of leaf miner, f. agromyzidae.
ANNUAL: One or a few tall leafy stems exceptionally reaching
one meter tall. A spring annual; few plants last beyond May in the
Sonoran Desert.
RANGE: Frequent throughout the Sonoran Desert in Arizona and Mexico on
hillsides and along better watered canyons. In drought years tansy mustard does
not germinate. Beyond Arizona this plant is widely distributed throughout much
of North America with a number of subspecies and varieties recognized.
FRUIT: Oblong capsules can vary considerably in size from 4 mm to
2 cm with corresponding variance in number of seeds.
FLOWERS: Flowers are small and may be cream or yellow; not very showy
except for an occasional plant with many flowers open at once. Again the usual
mustard flower morphology of 4-4-6.
UNARMED.
This is one of the mustard species used as a food plant by the caterpillars of Sara Orange-tip butterflies (Anthocharis sara).