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(also Bryatae), a class of spore-producing plants, or mosses, of the division Bryophyta. In contrast with other mosses, these are divided into a stem and leaves. The Musci comprise three subclasses—Sphagnidae, Andreaeidae, and Bryidae. They are annuals or, more frequently, perennials. Their development begins from spores from which germinates a lamelliform or, more often, branched, threadlike protonema with buds. The buds develop into green stems, which measure between a few millimeters and 0.5 m long; they have rhizoids and spirally arranged leaves. At the tip of the stem or on the lateral shoots there are female and male sex organs—the archegonia and antheridia. Fertilization occurs in the egg cell in the archegonium. The zygote develops into a sporophyte in the form of a sporogonium, consisting of a capsule with a spore case and, frequently, a mouth. The Musci also reproduce vegetatively.
Mosses of the class Musci are found on mountains and plains throughout the world, primarily in the tundra, forests, marshes, and the alpine mountain belt. Of the approximately 15,000 known species, more than 1,500 grow in the USSR. The most common mosses in forests are Polytrichum, Dicranum, and Mnium; in marshes, Sphagnum; in water, Fontinalis; and on rocky cliffs, Andreaea and Grimmia.
I. I. ABRAMOV