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California’s Rare Native Plants

From the California Native Plant Society

One of California's greatest natural treasures is its plants. Our state's mountain ranges, deserts, and extensive coastline, along with its unusual summer-dry climate, set the stage for the development of a complex and fascinating flora. The numbers themselves are impressive. About 6300 flowering plants, gymnosperms, ferns, and fern allies are native here, more than we find in the entire northeastern United States and adjacent Canada, an area ten times larger than California. Another thousand plants are weedy introductions to the state or escapes from gardens and agricultural fields. Although Texas has more genera and families, California's is the largest state flora in the nation.

One of the California flora's outstanding features is that more than one-third (36%) of its native species, subspecies, and varieties are endemics, plants that are restricted to a particular locality or habitat within the state. If we define the flora in terms of the California Floristic Province -- a unit including the Klamath Region of the northwestern part of the state and adjacent southwestern Oregon, along with that portion of California west of the Cascade-Sierra Nevada axis, and a part of northern Baja California -- then the degree of endemism (about 48%) is remarkable for a continental flora. Most of these endemics are rare or uncommon plants.

It has been argued that many endemics are plants becoming extinct because of old age, and that we are seeing their demise after a long evolutionary history. Others argued, quite to the contrary, that rare plants are merely evolutionary children that have not had time to spread. We now realize that while some endemics, such as the coast redwood, are indeed ancient relicts, most are of relatively recent origin.

Why does California have so many rare plants, especially so many that are endemic? The primary factor may be our climate, a regime of dry summers and cool, wet winters. Only in the Mediterranean Basin, Chile, and parts of Australia and South Africa do we find similar climates. Each is famous for its array of rare and endemic plants adapted to this unusual climatic regime. A second factor is topography and latitudinal diversity. Within the boundaries of this state are extremes -- from low, subtropical desert to habitats above timberline, from northern temperate rain forests in Del Norte County to arid succulent scrub in San Diego County. A third factor is the richness of geological formations and the resulting diversity of soil types. The broken topography of the state, combined with a tremendous diversity of climates and soil types, has resulted in ample opportunities for genetic isolation and speciation. The result has been impressive adaptive radiations within such groups as Arctostaphylos, Astragalus, Castilleja, Eriogonum, Gilia, Lupinus, Mimulus, Phacelia, and many genera in the Asteraceae, to name only a few. Most of our rare plants, then, are specialists, adapted to a particular combination of climate and substrate.

California's flora, especially its rare plants, are increasingly threatened by the spread of urbanization, by our conversion of land to agriculture, by alteration of natural hydrological cycles, by recreational activities and non-native plants and animals, and by pollution. The unique habitats that harbor rare plants are being destroyed. For example, 90-95% of vernal pools in the State are gone, and native grasslands in the Central Valley occupy but 1% of their former extent. About forty plants probably became extinct in the last century. Hundreds more are endangered and could perish if present trends continue. Arguments for conservation of rare plants, animals, and natural communities range from aesthetic, to moral, to economic or ecological. We strongly believe, however, that failure to conserve the biological diversity of our planet may well prove disastrous.

This text is quoted from the 5th edition of the CNPS Inventory, published February 1994.

Now, let’s look at examples of rare native plants :