General Features

Thallose bryophytes vary in size from a length of 20 cm (8 inches) and a breadth of 5 cm (2 inches; the liverwort Monoclea) to less than 1 mm (0.04 inch) in width and less than 1 mm in length (male plants of the liverwort Sphaerocarpos). The thallus is sometimes one cell layer thick through most of its width (e.g., the liverwort Metzgeria) but may be many cell layers thick and have a complex tissue organization (e.g., the liverwort Marchantia). Branching of the thallus may be forked, regularly frondlike, digitate, or completely irregular. The margin of the thallus is often smooth but is sometimes toothed; it may be ruffled, flat, or curved inward or downward.

Leafy bryophytes grow up to 65 cm (2 feet) in height (the moss Dawsonia) or, if reclining, reach lengths of more than 1 metre (3.3 feet; the moss Fontinalis). They are generally less than 3 to 6 cm (1.2 to 2.4 inches) tall, and reclining forms are usually less than 2 cm (0.8 inch) long. Some, however, are less than 1 mm in size (the moss Ephemerum). Leaflike structures, known as phyllids, are arranged in rows of two or three or more around a shoot or may be irregularly arranged (e.g., the liverwort Takakia). The shoot may or may not appear flattened. The phyllids are usually attached by an expanded base and are mainly one cell thick. Many mosses, however, possess one or more midribs several cells in thickness. The phyllids of bryophytes generally lack vascular tissue and are thus not analogous to the true leaves of vascular plants.

Most gametophytes are green, and all except the gametophyte of the liverwort Cryptothallus have chlorophyll. Many have other pigments, especially in the cellulosic cell walls but sometimes within the cytoplasm of the cells.

Bryophytes form flattened mats, spongy carpets, tufts, turfs, or festooning pendants. These growth forms are usually correlated with the humidity and sunlight available in the habitat.