rhizocarpous in British English
(ˌraɪzəʊˈkɑːpəs) or rhizocarpic (ˌraɪzəʊˈkɑːpɪk)
adjective1. (of plants) producing subterranean flowers and fruit
2. (of perennial plants) having roots that persist throughout the year but stems and leaves that wither at the end of the growing season