Rhizoids are a structure in plants and fungi that functions like a root in support or absorption.
In fungi, rhizoids are small branching hyphae that grow downwards from the stolons that anchor the fungus. They release digestive enzymes and absorb digested organic material.
In land plants, rhizoids are trichomes that anchor the plant to the ground. In the liverworts, they are absent or unicellular, but multicelled in mosses. In vascular plants they are often called root hairs, and may be unicellular or multicellular.