Rare Plant Program
Rare Bryophytes in California
James R. Shevock (from CNPS Inventory, 6th Edition, 2001)
Often overlooked by amateur and professional botanists alike, bryophytes (mosses, liverworts, and hornworts) are nonetheless highly important in the function of ecosystems and an important element in California's plant diversity. Before this edition, bryophytes had been excluded from the CNPS Inventory due to a lack of data necessary to determine which species are rare in California. 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. Because the majority of the 580+ mosses and 120+ liverworts are not endemic to California, most of our rare bryophytes occur as representatives of List 2 taxa (rare, threatened, or endangered in California but more common elsewhere).
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. Lacking roots and other complex water transport systems, bryophytes take in moisture directly through the surface of their cells, and can be highly susceptible to pollutants. Like the canary in the mine, bryophytes can alert us to changing conditions, sometimes at very local scales. Bryophytes also need to be able to adapt to California's many varied climates, from harsh desert environments to coastal rain forests. Many species have developed drought tolerance mechanisms and strategies, and some species are better adapted to prolonged desiccation than others, which leads to a better understanding of the distribution patterns observed in California bryophytes. So the annual amount of rainfall is not the key factor, by rather, the frequency of rain between periods of desiccation.
Lacking showy features like flowers, bryophytes are often perceived as difficult to identify. While some genera of mosses are taxonomically challenging, they are no more difficult to identify than some groups of flowering plants. With practice and knowledge of terminology for specific features used in identification, bryophytes can be identified by amateur botanists (see Fremontia 26(2):3-8, 1998). A very helpful feature of most bryophyte taxa is that they can be collected and studied in nearly any month of the year and be identified in their vegetative (gametophytic) state. In bryophytes, the reproductive structures (the sporophyte generation) are rarely required for species identification. However, most bryophytes require greater magnification than a hand lens for identification to the species level.
The conservation of California bryophytes is long overdue. With this edition, we are able for the first time to drop the 'Vascular' qualifier from the title and call it simply Inventory of Rare and Endangered Plants of California.
Bryophytes in the 6th edition
James R. Shevock is the Associate Regional Director, National Park Service, Pacific West Region, 600 Harrison St., Suite 600, San Francisco, CA 94107-1372.