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Riccia is a genus of liverworts in the order Marchantiales. One of the more than 100 species in this genus is the "slender riccia" (Riccia fluitans), which can be found floating in ponds, and is sometimes used in aquariums.
The plant body is a thallus that is not differentiated into root, stem and leaf. The thallus is dorsiventrally differentiated, and is dichotomously branched to form a rosette. The upper (dorsal) surface of the thallus is green with a mid-dorsal sulcus (furrow or groove) and tiny air pores.
The lower (ventral) surface has a mid-ventral ridge bearing a single row of multicellular scales on either side of the ridge. The scales are multicellular and violet due to a pigment anthocyanin. There are numerous unicellular rhizoids of two types on the ventral surface. One type is called smooth and the other type is the pegged or tuberculated rhizoids; these help in anchorage and absorption. The inner surface of the smooth rhizoids is smooth while that of the tuberculate rhizoid will have internal cell wall projections.
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