THILAPSI, BASTARD-CRESS, or mithridate-mustard, in botany: A genus of plants belonging to the class of tertradynamia, and order of siliculosos; and in the natural system ranging under the 39th order, Siliculosos. The pod is emarginated, obcordate, and polyspermous; the valves are boat-shaped and marginato-carnated. There are 12 species; of which six only are natives of Britain, the arvense, hirtum, campestre, montanum, perfoliatum, and burfa pastoris.
1. The arvense, treacle-mustard or penny-cress, has orbiculate pods, and leaves oblong, smooth, and scalloped. It smells like garlic, and has a white flower. 2. The hirtum, or perennial mithridate-mustard, has roundish hairy pods; the cauline leaves are sagittate and villous. 3. The campestre, or mithridate-mustard, has roundish pods, sagittate leaves, dentated and hairy. 4. Montanum, or mountain mithridate-mustard, has obcordate pods, smooth leaves; the radical leaves somewhat fleshy, obovate and entire; the cauline embracing the stalk, and the corolla being larger than the calyx. 5. The perfoliatum, or perfoliate treacle-mustard, has obcordate pods; the cauline leaves are smooth and subdentate; the petals of the length of the calyx, and the stalk branchy. 6. The burfa pastoris, or shepherd's purse, has obcordate pods; the radical leaves are pinnatifid.
The feeds of some of these species have an acrid biting taste, approaching to that of the common mustard; with which they agree nearly in their pharmaceutical properties. They are rarely made use of any otherwise than as ingredients in the compositions whose names they bear; though some recommend them in different disorders, preferably to the common mustard.