Bryophyta

Bryophytes are seedless, nonvascular plants that lack roots, stems and typical leaves. They are small in size, ranging from 2 to 20 cm. This is so because they lack vascular tissue necessary for transporting water and nutrients to parts of a plant that are not near the ground or near water. Bryophytes are very important ecologically because they can grow in new areas that have no soil, such as lava fields. This makes them Pioneer species, the first species to move into a new area. When some of these Bryophytes die they leave behind dead matter that begins the soil formation process. When enough soil builds up, other, larger, species can then move in. There are about 16,000 species in this division, which is broken down into two classes, mosses and liverworts.

Mosses

Moss is a simple rootless plant with leaflike growths in a spiral around a stalk. They are held in place by rootlike threads called rhizoids. Moss requires a damp environment, but does not need soil to survive. This makes it an important Pioneer species, as mentioned above. Moss and other Bryophytes go through an "Alternation of Generations." This is a cycle in which a sporophyte phase produces spores, which in grow into gametophyte, which produce gametes. Following fertilization, the resulting zygote grows into a new sporophyte. Thus, moss alternates between a spore producing phase and a gamete producing phase. This unique reproductive strategy allows the moss to increase it's numbers dramatically, while still creating genetic diversity within the population through sexual reproduction.

Liverworts

A liverwort is also a simple rootless plant, but has a flattened leaflike body. Liverworts get their name from their shape. They look like a liver (sometimes). Like moss, they grow in damp areas and are pioneer species.

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