Rare Plant of the Month: King’s gold

 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!

King’s gold (Tropidocarpum californicum) is not named for a mythical treasure. Its origins lie in King’s County, where most of the plant’s populations were originally found, and the gold color of its flowers. But it may be as rare as gold. This annual herb is endemic to (only found in) California and limited to a small area of King’s County and northwest Kern County. Its native habitat is moist to wet, alkaline, sandy clay soil within chenopod scrub below 600 feet. It lives among native species like saltbush (Atriplex) species, alkali heath (Frankenia salina), seablite (Suaeda nigra), and low barley (Hordeum depressum). 

Tropidocarpum is a small genus (with only four species) in the mustard family (Brassicaceae).  Two of the species (T. californicum and T. capparideum) are California endemics, one (T. gracile) is found in California and Baja California, and the fourth (T. lanatum) is native to Chile. This pattern of a genus with species found in the Mediterranean climate areas of California and Chile has been well-documented. Some of the species and genera associated with this pattern are found in moist soils/wetlands in and around the Central Valley, and the dispersal agent is presumed to be migratory birds. 

King’s gold has a California Rare Plant Rank of 1B.1, which means that it’s seriously threatened in California. This plant is threatened by inappropriate grazing, soil disking (a mechanical method of tilling soil), agriculture, and development. It’s known from nine occurrences, only six of which have been seen in the past 20 years. One of the historical occurrences has not been seen at the site since 1965, even though searches for it have been carried out. 

King’s gold is one of our rarest and most threatened California plants in an underappreciated habitat type (alkaline chenopod scrub) in a poorly conserved part of California (the San Joaquin Valley and its edges). Since most of the occurrences of this plant are on private lands, it is difficult to recommend a good place to see it, but King’s gold has been seen in the vicinity of the Kern National Wildlife Refuge. Visit the Rare Plant Inventory to learn more about King’s gold. 

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.