California Native Plant Society

Native Plants - Photo Gallery

Vernal Pools: A Vanishing Habitat

by Dianne Fristrom and John Game

Vernal pools are miniature ecosystems: natural depressions covered by shallow water for variable periods from winter to spring, they are typically dry for most of summer and fall. A diverse array of plants and animals adapted to a waterlogged spring followed by a parched summer have evolved that thrive under these conditions. Many of these are native species endemic to vernal pools or related wetland habitat. Because of the extreme environment there are relatively few introduced species that can compete with the natives. In addition to providing habitat for the resident species, vernal pools provide resting sites for migrating birds and foraging grounds for bald and golden eagles.

This essay was prompted by several new threats to California's already dwindling vernal pool sites. The new Merced campus of the University of California is slated to be built on the largest remaining pristine vernal pool habitat in the state; 10,000 acres of which will no doubt end up as part of a university town. Another 50 acre site, in the Sacramento Valley, Mather vernal pools is threatened by gravel mining interests. Both the above links indicate how you can help protect these remnants of a disappearing landscape.

All the photographs are by John Game except where otherwise noted.

A Vernal Pool with Downingia -- Multicolored Downingias are the signature plants of vernal pools. California, once so rich in vernal pool habitat, is the center of diversity for this genus with 13 different species. This pool from the Mt. Pinos area hosts the attractive Downingia bella.

A colorful melange of pink onions (Allium hyalinum) goldfields (Lasthenia sp.) and meadow foam (Limnathes douglasii). Photo from Table Mountain, Tuolumne County

Valley Downingia (Downingia pulchella) -- A relatively common and widespread Downingia found throughout the Central Valley and elsewhere. Photo from Springtown, Contra Costa County.
Photo by D. Fristrom.

Pincushion Navarettia (Navarretia myersii) -- Similar to the more common N. prostrata but with larger flowers and a longer tube, this one is a vernal pool endemic which may possibly be found on the proposed UC Merced site. Although not listed as endangered, it is very rare, occurring in four known sites. Photo from the Flying M Ranch, Merced County.

Meadow Foam (Limnanthes douglasii) -- Another common spring delight that frequently masses in vernal pools.

Tricolor Monkeyflower (Mimulus tricolor) -- One of several monkeyflower species that grow in wet places. This species with its distinctive color pattern prefers vernal pools. Photo from the Flying M Ranch, Merced County.

 Sand-spurrey (Spergularia macrotheca) -- A hardy plant of alkali vernal pools and related habitats. Photo from Springtown, Contra Costa County.
Photo by D. Fristrom.

Tadpole Shrimp (Lepidurus packardii) -- Not just for plants, vernal pools support a variety of animal life including tadpole shrimp, fairy shrimp and tiger salamanders to name a few. Tadpole Shrimp are listed as endangered under the Federal Endangered Species Act and occur on the proposed UC Merced site.

Rare and Endangered Vernal Pool Plants

The following are a few of the species federally or state listed as rare, threatened or endangered.

Contra Costa Goldfields (Lasthenia conjugens) -- While great displays of goldfields are a common spring sight in some areas, this species, endemic to vernal pools, is endangered. Photo from Warm Springs, Alameda County.

Succulent Owl's Clover (Castilleja campestris ssp. succulentus) -- This rare subspecies of field owl's clover is found on the proposed UC Merced site and only a few other places. Photo from the Flying M Ranch, Merced County.

Alkali Milkvetch (Astragalus tener var. tener) -- A rare species: Of the three subspecies of this plant, one is extinct and two are very rare. Photo from the Great Valley Grasslands State Park.

Chinese Camp Brodiaea (Brodiaea pallida) -- An endangered species occurring in only a few sites near Chinese Camp, Tuolumne County. It is endemic to vernal pools on serpentine. The inrolled staminodes (inset) with deeply notched tips distinguish this species.

Colusa Grass (Neostapfia colusana) -- An endangered grass endemic to California's vernal pools. This occurs on the proposed UC Merced site. The tuft at the top of the flower spike (inset) is distinctive. Photo from Yolo County.

About the Photographers

DIANNE FRISTROM is a retired geneticist from U.C.B. A botanical novice, she has a keen interest in photography and computer graphics. She recently combined these skills with the vast botanical expertise of John Game and Glenn Keator to produce "Wildflowers of the Bay Area" on CD-ROM. Dianne can be reached via email at

JOHN GAME works as a molecular biologist at the Lawrence Berkeley National Laboratory. He pursues an active interest in plants and botanical photography, especially photographs of Californian plants in the wild. Special interests include ferns and the family Liliaceae. John is active with CNPS, and is on the Board of the East Bay Chapter. John can be reached via email at

Photos and text © 2000 D. Fristrom and J. Game. All rights reserved.




Copyright © 1999-2018 California Native Plant Society. All rights reserved. Contact Us | Privacy