Riccia are small and thalloid, that is not differentiated into root, stem and leaf. Depending on species, the thallus may be strap-shaped with dichotomous branches or may form rosettes or hemirosettes, that may be gregarious and form intricate mats. The scales are multicellular and hyaline (glassy) in appearance, or violet due to the pigment anthocyanin. Rhizoids are nearly lacking in aquatic forms, but there are usually numerous unicellular rhizoids of two types on the ventral surface. The inner surface of the smooth rhizoids is smooth while that of the tuberculate rhizoid will have internal cell wall projections. It includes more than 100 species.