the season are more likely to be found at slightly higher elevations than later flowering species. Many vernal pool plants have buried seeds which accumulate in the soil. Different species are suited to different moisture levels, and as water evaporates from the edges of a pool, distinctive zonation of species can be seen. Most pools receive annual deposition of tree leaves, which are critical to maintaining local life due to leaf detritus. Many upland perennial plants are unable to withstand the period of flooding. Many wetland plants are unable to withstand the period of desiccation. Therefore, vernal pools are a distinctive habitat that provides a refuge from both terrestrial and fully aquatic plants. When dissolved carbon dioxide is depleted by daytime photosynthesis, vernal pool species like Howell's quillwort (Isoetes howellii) and pygmyweed (Crassula aquatica) collect carbon dioxide nocturnally using Crassulacean acid metabolism. Vernal pool basin habitats favor annual plants with some uniquely adapted perennials which suffer extensive mortality resembling annual reproduction. Annuals comprise approximately 80 percent of vernal pool flora. Listed below are some genera of the approximately one hundred vascular plant species associated with California vernal pool habitats. A typical pool will include only 15 to 25 species. Cosmopolitan aquatic flora quillworts (perennial) water clover (perennial) pillworts (perennial) water starworts succulents waterworts mousetail buttercups spikerushes (perennial) lilaea Vernal pool specialists stickyseeds calicoflowers button parsleys (perennial) snorkelwort false Venus' looking glass pincushion plants popcornflowers woollyheads Colusa grass Orcutt grass Solano grass Upland plants commonly found at vernal pools in California include yellow pansies, several sweet-scented clovers, yellow and bright lavender monkeyflowers, star lilies, and yarrow. Vernal pools are often threatened by development in the same way that other wetlands are. As a result, most pools have been converted into residential zones, roads, and industrial parks. That is why most extant pools occur on protected or private land such as national parks, and ranches. A large number of rare, endangered species, and endemic species occur in vernal pool areas. For example, the San Diego mesa mint, a highly endangered plant, is found exclusively in vernal pools in the San Diego area. Another example is the wildflower Lasthenia conjugens, which is found in limited parts of the San Francisco Bay Area. A third example is the herb Limnanthes vinculans endemic to Sonoma County, California. Fauna Many of the amphibians that breed only in vernal pools spend most of their lives in the