Vernal pools occur on coastal terraces in Southern California, alluvial deposits in the Central Valley, and elsewhere throughout the state. They are seasonal wetlands that occur in shallow depressions where there is an underlying impermeable layer that holds water after saturation. They typically fill with winter rains and dry up by early to late spring. Distinct rings of vernal pool vegetation may become apparent as the water dries. Pools remain dry through the summer months and are generally no more than 18” deep at maximum inundation, developing the flora of vernal marshes when deeper. Unique plant and animal species are adapted to this cyclical process of wetting and drying, including coyote thistles, clam shrimp, the endangered Santa Barbara tiger salamander (north county), and many species of birds. Many of these species of plants begin their lives underwater and finish their life cycles in dry, exposed soil. Over 90% of vernal pools have been destroyed due to agriculture, development, draining, weed invasion and other disturbances.
Common spikerush
| Eleocharis macrostachya | Cyperaceae (sedge family) |
Rhizomatous perennial, 15-60 cm (5-24 in). Usually found in heavy soils such as the lower portions of vernal pools, where it usually dominates. Brown spikelets form at the tip of each stem. Two similar species, Eleocharis montevidensis and E. parishii also occur in the area, although they are less common. In badly degraded pools, E. macrostachya may be the only native species present.
Needle spikerush
| Eleocharis acicularis | Cyperaceae (sedge family) |
Weakly rhizomatous perennial herb, 1-60 cm (0.4 -25 in) usually under 3 inches in height. Sometimes forming mats of thin flowering stems, two varieties occur in the area, E. acicularis var. acicularis and E. acicularis var. occidentalis, although it is difficult to distinguish between the two. This plant is wide-ranging, occurring in Europe, North and South America, and Asia. It is occasionally used in the freshwater aquarium trade as a perennially submerged plant, but our local forms are adapted to the summer drought and desiccation common to vernal pools.
Coyote thistle
| Eryngium sp. | Apiaceae (carrot family) |
Annual or perennial, prostrate herb, to 30 cm (12 in), with acutely spiny leaf tips, bracts, and sepals. They can begin their life cycle underwater, where they have hollow, inflated stems. This plant is relatively abundant locally, occurring in vernal pools and slight depressions wherever there are clay soils along the coastal mesas. Locally, the species has historically been referred to as Vasey’s coyote thistle, Eryngium vaseyi, but needs more investigation, as some consider it a possible new, undescribed species (Ferren, personal comm.).
A second species, the coastal eryngium (Eryngium armatum) is less common, and grows around the upper edges of vernal pools rather than in the basins. It occurs from Mendocino County southward and reaches its southern limit in Isla Vista at the Camino Corto Open Space. We have expanded this species’ range by growing it from seed and outplanting at NCOS.
Lemmon’s canary grass
| Phalaris lemmonii | Poaceae (grass family) |
Annual grass, 20-75 cm (8-30 in). This locally rare grass can sometimes be seen growing out of shallow water in vernal pools, or around the moist edges. It has a large, plump seed that is heavily predated upon by non-native rats, and may have been a Chumash food when it was common. A pernicious perennial weed in the same genus, Phalaris aquatica, Harding grass, is common and spreading in the region.
This exotic species was purposefully sown at the site of the unique vernal pools at More Mesa for cattle feed, where it persists today to the detriment of the native flora. Another uncommon native annual vernal pool grass, pacific foxtail (Alopecurus saccatus), occurs in our local area, and displays attractive, orange anthers.
Short woollyheads, woolly marbles
| Psilocarphus brevissimus | Asteraceae (sunflower family) |
Annual, to 5 cm (2 in), but usually less than 0.5 inch. It resembles little wool-like balls. This distinctive vernal pool plant is uniquely adapted to the flooding and drying of vernal pools, and is found in these habitats throughout the state. A slightly larger, similar species, Psilocarphus tenellus, also occurs locally and state-wide in the same habitats, but is less common.
Popcorn flower
| Plagiobothrys undulatus | Boraginaceae (borage family) |
Prostrate annual, 8-30 cm (3-12 in), with small, white flowers. Found in vernal pools and similar seasonally wet places with clay soils. Sometimes concentric rings of this plant can be seen in vernal pools as the pools dry and water levels recede. A second species of popcorn flower, Plagiobothrys bracteatus, also occurs in vernal pools of the area, but is less common. The two can be differentiated by their seeds, called nutlets. Nutlets of bracteatus are about 1/3 the size of those found on P. undulatus and bear a different scar.