Bryophytes are small, seedless, nonvascular plants. Because they lack vascular tissue, they also lack true stems, leaves, flowers, and roots. They grow low to the ground and absorb water by osmosis. The three major groups of bryophytes are mosses, liverworts, and hornworts. Liverworts have prominent gametophytes, which is the sexual phase in the life cycle of plants. Thalloid liverworts consist of a flattened mass of tissue (thallus).
Water liverwort (Marchantia aquatica) is one of the largest thalloid liverworts. It is found across North America and in Europe. It grows on moist or wet soil in swamps, calcareous fens, wet meadows, cliffs, springs, disturbed areas, and recently burned areas. It often forms colonies of overlapping plants, sometimes creating extensive mats. It can be a pest if allowed to invade a greenhouse.
Liverworts reproduce both sexually and asexually. The asexual reproductive structure of water liverwort is a splash cup (gemma cup) that is produced on the upper surface of the thallus. The cups are green, circular, and shallow, and contain a few gemmae. The gemmae are dispersed when they are splashed out by raindrops. Each gemma can produce one or two plants if it lands on soil.
Water liverwort is distinguished from its close look-alikes by a dark, midrib-like furrow on the thallus that is uninterrupted and conspicuous.