Althaea (Gr. to cure), a genus of plants belonging to the natural order malvaceae. They have a double calyx, the outer whorl with from 6 to 9 sepals, and the inner with 5. A. officinalis is the marsh mallow, the knowledge of which in medical botany is of great antiquity. The mucilaginous roots and leaves of this plant are used in all cases in which emollient or demulcent substances are required. It is a perennial plant, with a white, fleshy root, 12 or 15 inches long. The stems are 2 or 3 feet high, and covered all over with a soft down. The leaves are also covered with down, which gives the whole plant a hoary aspect. The leaves are soft and stalked, the flowers of a pale rose color, appearing in very short clusters from the axil of the leaves. The corolla is like that of the common mallow. The demulcent lozenges sold under the name of pate de guimauve are made of A. officinalis; they are made in large quantities in the south of France, particularly at Marseilles. The hollyhock, A. rosea, grows wild in China. (See Hollyhock.) - Althaea is a common name of the ornamental shrub hibiscus Syriacus, also called rose of Sharon. (See Hibiscus.)