Descurainia incana (Bernth. ex Fisch. & C.A. Mey.) Dorn
Habitat: Calcareous gravels, prairies, and roadsides.
Range: Labrador south to Maine, Connecticut, and Massachusetts, west to British Columbia and Alaska, south to New Mexico and Texas
Aids to Identification: Richardson’s tansy-mustard has small, yellow flowers with 4-petals. The linear-cylindric fruits (called siliques) are 5-10 mm long and are on strongly ascending pedicels. The leaves are once-pinnately divides with leaflets that are entire to lobed on the margins. The image on the right shows Descurainia sophia which is naturalized in Maine. It differs from D. incana by having longer siliques (1.5-2.5 cm), which are not as strongly ascending as D. incana, and the leaves are 2-3 times pinnately divided.
Ecological characteristics: This is a pioneer species and does not persist in the same location for a long period of time. It is likely that the former locations for this plant have grown in thus excluding Richardson’s tansy-mustard.
Phenology: Flowering and fruiting July through Septemeber.
Synonyms: Descurainia richardsonii (Sweet) O.E. Schultz; Sisybrium incanum Bernth. ex Fisch. & C.A. Mey.; Sophia richardsonii (Sweet) Rydb.
Known Distribution in Maine:This rare plant has historically been documented from a total of 6 towns in the following counties: Aroostook, Piscataquis, Somerset.
Reason(s) for rarity: Calcareous habitat is scarce in Maine and the plant doesn’t persist in the same spot for long periods of time.
Conservation considerations: Unknown, has not been seen in Maine recently.