XanthorhizaXan`tho*rhi"za\, n. [NL., fr. Gr. xanqo`s yellow + "ri`za root.] (Bot.) A genus of shrubby ranunculaceous plants of North America, including only the species Xanthorhiza apiifolia, which has roots of a deep yellow color; yellowroot. The bark is intensely bitter, and is sometimes used as a tonic.