A subclass of acrocarpous mosses with several unique characteristics; they are sometimes included in a separate class (Andreaeopsida). The plants are small and characteristically black or dark brown. The protonema is thalloid. The capsules differ from those of other mosses in that they open by (usually 4) longitudinal slits. They form scattered patches on rocks in mountainous and Arctic regions.
Subjects: Plant Sciences and Forestry.