Federally listed as threatened; State-listed as endangered; California Native Plant Society List 1B.1
About Colusa grass
Colusa grass is endemic to California, with a broader geographic range than the other Orcutt grasses. It is found mainly in the southern Sierra foothills, with additional populations in the San Joaquin and Sacramento Valleys. It has been found in Colusa, Glenn, Merced, Solano, Stanislaus, and Yolo Counties. There are no records of Colusa grass in the Natomas Basin, but small patches of suitable vernal pool habitat are present on its eastern border. The closest known occurrence of Colusa grass to the basin is approximately 10 miles (16 kilometers) southwest in Yolo County, near the Yolo-Solano County border.
Colusa grass grows in large, deep vernal pool bottoms at elevations below 660 feet (200 meters). It has been found in pools of widely varying size, from 0.02 to 618 acres (0.008 to 250 hectares). Depending on geographic region, it is associated with the rim of alkaline basins, northern hardpan and claypan, or acidic alluvial soils.
Colusa grass is a small annual herb in the grass family (Poaceae) that blooms May through August. It is also a member of the Orcuttieae tribe, which consists of the Orcutt grasses and plants in the Tuctaria genus. Colusa grass relies on a flood-drought cycle, surviving dry summers in seed form and sprouting with winter and spring rains. Like the Orcutt grasses, Colusa grass produces different leaves depending on whether it is in an aquatic or terrestrial stage of life. Compared with other Orcuttieae, Colusa grass has a short underwater growth stage. Colusa grass produces an intensely aromatic fluid that coats its leaves—a possible defense against grazing herbivores. It generally does not grow with many other species, growing instead in single-species stands.