A type of primitive plant in the division Bryophyta which does not have a vascular system and lacks roots. Peat mosses (class Sphagnopsida) are plants which form spongy, pale-green mats in still freshwater environments like pools, bogs, swamps, and the shores of lakes and ponds. Class Andreaeopsida (including the granite mosses) are blackish-green plants with rhizoids which grow on siliceous rocks (such as granite) at high altitudes and soils in cold regions. True mosses (class Bryopsida) are a large and diverse group of plants that tend to consist of tiny, branching filaments, rhizoids, and reproductive organs at the tips which release spores. They mostly grow on tree branches, rocks, and bare soil, but may also grow in freshwater streams or in arid regions.