LEAFY LIVERWORT

also called Scale Moss, any of numerous species of liverworts (class Hepaticae), generally of the order Jungermanniales, in which the plant body is prostrate and extends horizontally in leaflike form with an upper and lower surface. About three-quarters of all liverworts species belong to this order. Most leafy liverworts are found in moist habitatsin swamps and bogs and in damp forests, where they grow on rotted logs or in damp soil. Others are found in colder environments, and still others are aquatic. The plant's leaves are spirally arranged around the stem, most often in rows of three. The leaves are usually lobed, and those of some species may have toothed or fringed edges and may curve upward. New growth covers the old, which then dies for lack of light. The mature gametophyte of the leafy liverwort can be either dioecious (each individual bears either male or female reproductive structures) or monoecious (each individual bears both male and female reproductive structures). The fertilized egg eventually develops into the sporophyte, which remains dependent on the gametophyte for water and nutrients. The sporophyte's spore-containing capsule (sporangium) is usually attached to the gametophyte by an elongate setae. The sporangium ruptures and releases spores, which germinate, ultimately into the gametophyte. The gametophyte remains attached to the substratum by way of filamentous rhizoids. The greatest number and variety of leafy liverworts are found in tropical Central and South America and in the Malay Archipelago. Plagiochila, a very species-rich genus, is found throughout the world. The large family Lejeuneaceae, which is extremely diverse in the tropics, shows an extraordinary variety of form and ecology. Many species of Frullania are able to tolerate drying and can revive after drought, thus allowing them to grow in areas where rains are seasonal.