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
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
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
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
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
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,
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
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
of the Bay Area" on CD-ROM. Dianne can be reached via
email at Fristromwildflowers-cdrom.com.
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
Photos and text © 2000 D.
Fristrom and J. Game. All rights reserved.