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a genus of plants of the class Hepaticae (liver-worts). The plants have green, ribbonlike, prostrate thalli, which are up to 10 cm long and 1-2 cm wide. The air chambers inside the thalli are filled with palisade tissue; there are barrel-shaped pores above the air chambers. On the upper side of the thallus there are cupules for asexual reproduction; under the thallus there are rhizoids, which attach the plant to the soil, and scales. Antheridia form on the upper side of the umbrella-shaped male branches, and archegonia develop beneath the radiating female branches. There are two species in the USSR. The more common species is Marchantia polymorpha, which grows in the northern hemisphere wherever there is moist soil (usually in marshes or on fertilized soil.).