Bryopsida

• Bryopsida consists of 11,500 species and is by far the largest of the eight moss classes.Photos.com/Photos.com/Getty Images
  
  The Bryopsida class includes approximately 98 percent of all moss species. One of the only consistent attributes among the various mosses in this class is the presence of a peristome. The arrangement of these toothlike appendages form compartments in which reproductive spores are gradually discharged. Acaulon Moss, Largespore Ulota Moss and Pohlia Moss are all in the Bryopsida class and can be found growing in damp environments in North America.
  
  

Sphagnopsida

• The Sphagnopsida class is comprised of mosses that grow in peat bogs and mires. Because bogs depend on precipitation and have poor drainage, they create a favorable environment for Sphagnum plants. Peat mosses generally consist of a main stem, spreading branches and hanging branches. They do not have roots. Peat mosses acidify their surroundings by releasing hydrogen ions into the wetlands they inhabit. Peat mosses are most commonly found in the Northern Hemisphere.
  
  

Andreaeopsida

• There are roughly 100 known Andreaeopsida mosses. They thrive in cool climates and tend to attach themselves to siliceous rock. Andreaeopsida mosses are black or red. The leaves of these mosses are extremely small and form multi-ranked arrangements. This brittle moss can be recognized in the wild by rubbing one's hand across the top and finding small fragments stuck to the palm.
  
  

Polytrichopsida

• Polytrichopsida mosses are larger than most others. The Dawsonia superba specie (found in Australia) can stand nearly 1.6 feet tall. A large central stem, complete with the presence of leptoids (sugar-conducting cells) and hydroids (water-conducting cells), characterizes this class of moss. Polytrichopsida leaves typically surround the stem and are recognizable because of their distinct midrib-like structure.
  
  

Takakiopsida

• Takakiopsida mosses were discovered in the Himalaya mountains in the 19th century. The species of this unique genus only have four chromosomes per cell, which is among the lowest known chromosome count of land-based plants. Takakiopside mosses have green shoots that extend from slender horizontal rhizomes. These shoots are extremely brittle and grow no larger than 0.3 inches long.
  
  

Andreaeobryopsida

• Andreaeobryopsida was considered a part of the Andreaeopsida class until 2000 when scientists noticed distinctions in the two classes. Andreaeobryosida mosses differ because they are dioicous and possess seta. Dioicous mosses have male and female reproductive organs on separate plants. Seta are bristles that support the capsule of a moss.
  
  

Oedipodiopsida and Tetraphidopsida

• The Oedipodiopsida and Tetraphidopsida classes of moss are the most rare. The Oedipodiopsida class contains only the Oedipodium graffithianum species. This type of moss is typically found in the cooler climates of North America, South America, Eurasia and islands in the northern Atlantic. The Tetraphidopsida class has two genera, Tetraphis and Tetrodontium. Both contain two species. Tetraphidopsida mosses are characterized by their rhizoid bases and chlorophyll abundance. They are commonly found in the Northern Hemisphere and are rare in the Southern Hemisphere.