Rare Plant Program
Introduction to the Inventory, 6th Edition
California's flora is unusually diverse. About 6,300 vascular plants – ferns and fern allies, gymnosperms, and flowering plants – are native to California, more than we find in the entire northeastern United States and adjacent Canada, an area ten times as large. There are also an estimated 750 native bryophytes – mosses, liverworts, and hornworts. The wonderful diversity of our landscapes sets the stage for this diversity of plant life. Within the boundaries of this state are extremes – from deserts below sea level to high alpine meadows, from rain forests to arid succulent scrub. In addition, our state's complex geology and topography produces a wide diversity of soil types. Widely contrasting habitat conditions closely juxtaposed produce ample opportunities for genetic isolation and speciation. The result has been impressive adaptive radiations within such groups as Arctostaphylos, Astragalus, Castilleja, Eriogonum, Lupinus, Mimulus, and many genera in the Asteraceae, to name only a few. Indeed, most of our rare plants are specialists adapted to a particular combination of climate and substrate and many are members of one of these recently diverging groups.
In addition to being unusually diverse, California's flora is outstanding in that more than a third of its native species, subspecies, and varieties are endemics – restricted to a particular locality or habitat within the state. The high proportion of endemics in our flora, a consequence of our unusual climate and landscape, gives us a special responsibility – protecting a large number of species that occur nowhere else in the world.
Human impacts, including urbanization and agricultural conversion, alteration of natural processes, and the introduction of nonnative plants and animals, threaten our rich flora. Rare plants are inherently vulnerable, since even small losses can tip a rare species toward extinction. Likewise vulnerable are species that are dependent on specialized habitats that are being fragmented, degraded, or completely eliminated. For example, 90-95% of our vernal pools are gone, and native grasslands in the Central Valley occupy only 1% of their former extent. Much of the coastal scrub of southern California has been urbanized, as have other lowland regions of the state. More insidious and operating over the longer term, human-caused alterations in the global climate threaten to fundamentally alter the landscape of California.
We rely on information as our most effective conservation tool. For over 30 years, the CNPS Inventory has served as a forum for regular review of the status of rare plants by a broad body of scientists and field botanists, and as a means of bringing that critical information to the attention of regulatory agencies and the concerned public. In this way, the Inventory supports both proactive conservation planning and effective enforcement of environmental laws that protect rare species. The Inventory also builds a foundation for stewardship and conservation action by celebrating the richness of California's rare flora and by broadening our understanding and appreciation of these unique and endangered plants.
The Inventory has been maintained by CNPS since 1968 and is now in its 6th edition. It is available both in printed and electronic versions. To order a copy, visit our bookstore or contact CNPS at 916/447-2677.