By Ellen Dean
The Rare Plant of the Month blog highlights one of the rare plants in the CNPS Rare Plant Inventory (RPI), an invaluable resource that has helped protect approximately 2,450 rare plant taxa in California since 1974!
In celebration of the designation of Sáttítla Highlands National Monument in January of this year, we’re highlighting a rare plant from this newly protected land, which is located east of Mount Shasta in far northeastern California. Columbia yellow cress (Rorippa columbiae) is a small, perennial herb from creeping roots in the mustard family (Brassicaceae). Wait, was that a needle scratch I heard? Mustard often makes people think of black mustard, the invasive plant that kills off native plants with its aggressive growth and becomes wildfire fuel once it goes dormant.
Columbia yellow cress, however, is a California native plant and none of those things. Its yellow, four-petaled flowers can appear from May through November, depending on location, and are covered with short soft hairs, It even has short hairs on its fruits, an important characteristic that distinguishes Columbia yellow cress from other species of Rorippa (yellow cress) in California. Occurring in California in Siskiyou, Modoc, and Lassen counties (and, perhaps, Humboldt County) it ranges north to Washington state where it is known from the Columbia River watershed, the source of its name (Rorippa columbiae).
The genus Rorippa is known for occurring in habitats such as the sides of creeks or lakes, marshes, and wet meadows in soil that is at least seasonally wet. True to form, Columbia yellow cress grows in vernal pools or depressions and along the edges of lakes, ditches, and creeks. Within the Sáttítla Highlands national monument, scientists have observed yellow cress on the shores of Medicine Lake, which is part of the Medicine Lake Highlands formed by the Medicine Lake Volcano. Yellow cress seems to particularly enjoy volcanic soil and is often found on volcanic soils elsewhere in its distribution.
In the CNPS Rare Plant Inventory, Columbia yellow cress is ranked 1B.2 (rare, threatened, or endangered in California and elsewhere). According to NatureServe, it is ranked Vulnerable in Oregon and Critically Endangered in Washington, where it is State-Listed as Threatened. Threats to this species include water diversion, development, grazing, off-road vehicles, and competition with non-native plants (hopefully not black mustard) .
Columbia yellow may not emerge in years with low rainfall; this can make it difficult to locate. Last year it was seen near Windy Hollow, Lassen National Forest, west of Hwy 44 in Lassen County. Visit the Rare Plant Inventory to learn more about Columbia yellow cress.
Ellen Dean is Associate Rare Plant Botanist at CNPS, helping complete rare plant profiles. In a previous life, she was an herbarium botanist, performing plant IDs, leading collecting field trips, training students in plant identification, curating the herbarium, and publishing taxonomic papers.
The post Rare Plant of the Month: Columbia yellow cress appeared first on California Native Plant Society.
