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Contra Costa Goldfields

Contra Costa Goldfields

Lasthenia conjugens
and
Solitary bee pollinator
Andrena submoesta


The dime-sized Contra Costa Goldfields is a vernal pool plant with a short, spring bloom cycle. These infrequent pools are the result of captured rainwater that slowly evaporates. The plant groups often springing from this short cycle ecosystem may include Downingia , meadowfoam, and a carpet of yellow goldfields (Lasthenia conjugens.) A sunflower-related plant, goldfields depends on vernal pool habitat and its solitary native California bee pollinator, (Andrena submoesta.)

Often mistaken for flies, these small, dark, solitary bees use either burrows or existing cavities for nests and leave behind a food supply to insure their offspring's survival. The female tunnels into the soil during the flower's short bloom cycle, makes a main hall, and digs side tunnels and brood cells for her young. She then coats the brood cell with a waterproof secretion and files into the daylight to collect pollen from the goldfields all the while being the solitary pollinator of the Contra Costa goldfields. The female carries large loads of pollen on her hind legs equipped with specialized hairs. Returning to her burrow, she lays a single egg on a very small ball of nectar and pollen and then closes the brood cell. Each burrow may contain five or six brood cells and she may lay as many as 30 eggs which were fertilized in a single encounter with a male bee. Overwintering in the brood cell, the young bee has a ready food supply upon its emergence the following spring an d thus the cycle begins anew.

Listed as both a state and federally endangered plant, goldfields needs special protection. Preservation and management of habitat may not be enough safekeeping since the preserved zones are often surrounded by development. In addition to providing sanctuary, open space and livestock grazing to keep the European grasses from choking out the flowers are also needed. In Contra Costa County, shrinking wetlands have reduced the goldfields' habitat to a single location located near Highway 4 near Hercules.

A debt of gratitude is owed to Muir Heritage Land Trust and the University and Jepson Herbaria, University of California, Berkeley for assistance with plant material specimens. Additional help with insect specimens was provided by the Academy of Sciences, San Francisco.

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