The botanical history of bryophyte collecting in California spans nearly 150 years, but for the most part these efforts have not been systematic. It has taken additional fieldwork to obtain enough specimens to determine the likely distribution of species at the county and province level. For the first time, we have sufficient information to evaluate this plant group with regards to rarity and endangerment and the need for their conservation in California. This is due to the development of a bryoflora of California by Dr. Dan Norris, based on his extensive field collecting, along with contributions from other knowledgeable experts. Bryophytes grow on a wide variety of substrates, including exposed soil, rocks, and trees, and some are even completely aquatic.
Bryophytes generally have much wider geographic ranges than vascular plants.
However, they are typically restricted to more specific microhabitats, causing them to often have widely disjunct distribution patterns, and are prone to localized extirpations. Like the flowering plants, some are common and widespread while others are quite rare. Examples of California endemic and rare mosses include Mielichhoferia tehamensis, Orthotrichum shevockii, O. spjutii, Schizymenium shevockii, and Triquetrella californica. Rare liverworts include Geothallus tuberosus and Sphaerocarpos drewei . Vulnerability of bryophytes to environmental changes make them ideal candidates in both air and water pollution studies, as well as excellent indicators of climate change.