Colusa grass is a California endangered plant species, which means that killing or possessing the plant is prohibited by the California Endangered Species Act (CESA). Colusa grass is an annual grass that grows to about 7-30 centimeters tall. It flowers in the summer months with cylindrical, dense inflorescences resembling small ears of corn.
Colusa grass is a vernal pool plant, so its biology is adapted to the hydrology of these ecologically unique systems. Colusa grass produces aquatic seedlings that can remain dormant for three to four years, germinate in the late spring, and flower during the summer months. Years of above average rainfall will produce much larger populations, and in some cases populations that have disappeared for one to two years will reappear. Colusa grass is also listed as threatened under the federal Endangered Species Act, and is included in the Recovery Plan for Vernal Pool Ecosystems of California and Southern Oregon completed by the U.S. Fish and Wildlife Service in 2005.
Colusa grass is usually found growing in single-species stands in alkaline basins of Sacramento and San Joaquin valleys, as well as acidic soils along the eastern San Joaquin valley and the Sierra Nevada foothills. It is difficult to know the historic range of Colusa grass because so much of California’s vernal pool habitat in the Central Valley has been destroyed. According to the California Natural Diversity Database (CNDDB), there are 42 occurrences of Colusa grass believed to still exist, and 18 more occurrences that are presumed to have been extirpated.
Like other vernal pool species, the biggest threat and reason for decline of Colusa grass is habitat loss and fragmentation caused by agriculture and development. Development can lead to direct removal of vernal pool habitat, and development adjacent to vernal pools can also indirectly affect habitat by altering hydrology and creating new sources of runoff into the ecosystem. Other significant threats include damage from nearby herbicide applications, contamination of groundwater, grazing, invasive native and nonnative plants, vandalism, and large outbreaks of grasshoppers. Occurrences that have fewer than 100 individuals are also threatened by low genetic diversity.
Currently, four occurrences in six pools are protected by The Nature Conservancy. One of these protected occurrences is at Jepson Prairie Preserve in Solano County, and the other three are at Flying M Ranch in Merced County. There are also three occurrences on federal land, with the rest of the occurrences on privately-owned land. The most important priority to ensure conservation of Colusa grass is to protect current habitat from future agricultural and urban development. Several other priorities for conserving vernal pools in general have been identified in the Recovery Plan for Vernal Pool Ecosystems of California and Southern Oregon. Priorities specific to Colusa grass include conducting research to better understand its reproductive biology and ecology.
CDFW may issue permits for Colusa grass pursuant to CESA, and you can learn more about the California laws protecting Colusa grass and other California native plants. Populations of Colusa grass occur in CDFW's North Central Region, Bay Delta Region, and Central Region. More information on Colusa grass is also available from the U.S. Fish and Wildlife Service Species Profile for Colusa grass.