(Marchantiopsida) A class of the * Bryophyta containing the thallose and leafy liverworts, which number about 10 050 species in about 295 genera. The Hepaticae differ from the * Musci (mosses) in showing marked dorsiventrality in the gametophyte. The antheridia and archegonia may be borne on the surface of the thallus or on fleshy stalks (see gametangiophore). The capsule of the sporophyte, which contains sterile elaters as well as spores, matures before the seta lengthens, while in mosses the reverse occurs. The capsule does not contain a central pillar of sterile cells (columella) as is found in the Musci and Anthocerotae. The Hepaticae is divided into some five orders, of which the Jungermanniaies (8000 species) and Marchantiales (2000 species) are the largest. A typical thallose liverwort is Pellia, which consists of a flattened dichotomously branching and frequently deeply lobed thallus. The ventral surface has numerous unicellular rhizoids growing from the area around the midrib. The leafy liverworts (suborder Jungermanninae) generally have three rows of leaves arising from a prostrate stem, although usually only the two dorsal rows are fully developed. |
