Antioch Dunes Evening-primrose

Oenothera deltoides ssp. howellii

Description

Stems of the perennial Antioch Dunes evening-primrose, Oenothera deltoides ssp. howellii, spread along the ground to 1 ft (0.3 m) or more during the first spring and rarely produce blooms. Oblong leaves are deeply cleft into narrow lobes, giving a feather-like appearance. Buds are sharply pointed. In the second year, the prostrate stems spread further and produce an abundance of large white flowers that flush pink with age. The plants grow to approximately 3 ft (1 m) in diameter by the second year and can reach nearly 3 ft (1 m) in height. After producing an abundance of seed capsules, most of the plants grown in cultivation die off during their second winter, although some continue into a third or fourth year. The subspecies is best regarded as a perennial, albeit probably short-lived.

The Antioch Dunes evening-primrose is vespertine; the flowers open in early evening and close by mid-morning. In the garden, the plant flowers from March to May and briefly in September. This Oenothera is self-incompatible and thus requires cross-pollination to produce sound seed. Numerous smooth buff-to black-colored seeds are produced in the capsule. Bees are believed to be the primary pollinating agent at Antioch. Although hawk-moths were not known on the dunes until 1983, they have been reported as pollinators of other Oenothera species.

Habitat

Observations of cultivated plants suggest that seedlings of the Antioch Dunes evening-primrose will not reach maturity where adult plants have recently matured and died, and that fresh sand is necessary for seedling re-establishment in such areas. Seedlings that germinated where adult plants had previously grown perished after attaining a height of approximately 6 in (15.2 cm), which suggests that the evening-primrose exhausted the nutrients within the soil where the preceding generation matured.

Sandy soils are notorious for their poor nutrient storage capacity. This is because sandy soils not only generally lack the quantity and appropriate kinds of clay particles, but also the organic matter which attracts exchangeable nutrients. Research has confirmed that in the Eureka Dunes in Inyo County, generally sandy dune substrates have low nutrients and, thus, it is assumed low fertility. The germination of seed is dependent on the optimal coincidence of burial depth, moisture, and temperature. That the Antioch Dunes evening-primrose produced numerous seedlings in recently disced areas would tend to indicate that the seeds respond favorably to disturbance or burial and not necessarily the deposition of nutrient-laden fresh sand.

The wallflower evidently does not require a periodic refreshment of sand in cultivation reported as necessary for the establishment of evening-prim-rose seedlings. Wallflower seedlings have moved from the sandy bed to several black soil or gravelly locations within the garden, indicating that, at least under garden conditions, the plant does not require sandy soil.

Distribution

The only natural stands of evening-primrose exist on the dunes near Antioch. Nonetheless, the sub-species has been introduced into at least three different localities by Regional Parks Botanic Garden personnel since 1970. In addition, they introduced evening-primrose seed onto the dunes at Point Reyes National Seashore in Marin County. Although the experiment failed at Point Reyes, the Oenothera became naturalized at Brannan Island and thrives there today. In 1978, two small colonies were started on Brown's Island in Contra Costa County.

In 1978, botanists counted about 1,000 living plants at the 27-acre (11-hectare) site of the only known population. Few seedlings were observed. After the site was acquired by the U. S. Fish and Wildlife Service (FWS), the evening-primrose began to recover. In 1984, 5,132 individuals were counted, and in 1988, 4,320 plants were located, down from previous counts due to an unexpected disturbance of the habitat.

Threats

Heavy industrialization, sand mining, and conversion of adjacent lands to agriculture have caused a steady decline in the amount of available habitat. Weedy exotic plants have also invaded the habitat, crowding out native species. For years, portions of the dunes were used for dumping garbage.

In active dune systems undisturbed by humans, sand is deposited and redeposited by the wind. The degree to which pristine Antioch Dunes resembled this type of dune system is open to speculation. Considerable evidence exists that indicates that the Antioch Dunes were stabilized in historical times with only limited blowout areas. Nevertheless, the invasion of the dunes by exotic vegetation has doubtlessly further stabilized the soil and increased the competition for resources and thus poses a significant problem to those species requiring or disturbed sand for survival. To what degree this may affect the reproduction and mortality of the evening-primrose is unknown.

The reduction of habitat within the Antioch Dunes by man may have adversely affected the pollinators of the evening-primrose. The self-incompatible evening-primrose is probably pollinated by bees and/or hawkmoths and, therefore, the possibility of reduced fecundity exists. The reduction of habitat by sand mining, exotic vegetation, and industry is probably of greater direct consequence to the plants. Plants that are infested with beetles attaching to leaves and flower buds showed reduced reproductive output. Beetles feed on petals, pollen, and seed pods.

Periodic discing, hiking, and off-road vehicles abuse on the dunes have also adversely affected the evening-primrose and its habitat. While only firebreak discing remains a threat, the destruction of mature and seedling plants by discing may open up areas for establishment of seedlings.

Botanists have observed the wallflower growing in steep areas of unstable sand. These slopes generally are not as densely vegetated, which may enable the wallflower to compete better for nutrients and water. However, the wallflower grew at one time on flat terrain on the McCullough property.

Conservation and Recovery

The recovery of the evening-primrose will depend on the larger effort of restoring the ecosystem. In 1980 the FWS acquired 70 acres (20 hectares) of the Antioch Dunes, adding this parcel as a satellite to the San Francisco Bay National Wildlife Refuge. This acquisition allowed for needed management actions to eliminate encroaching plants, to restore sand removed by mining operations, and to clear away refuse. As new parcels of adjacent land become available, the FWS will consider adding these to the Refuge.

The East Bay Regional Botanic Gardens cultivates this plant and has dispersed seed to three new sites: Brannon Island State Recreational Area (Sacramento County); Point Reyes National Seashore (Marin County); and Brown's Island (Contra Costa County). According to the latest surveys (1984), the Brannan Island population is the only transplanted population that appears to be thriving.

Contact

Regional Office of Endangered Species
U.S. Fish and Wildlife Service
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

References

Howard, A. Q., and R. A. Arnold. 1980. "The Antioch Dunes-Safe at Last?" Fremontia 8: 3-12.

Klein, W. M. 1970. "The Evolution of Three Diploid Species of Oenothera Subgenus Anogra (Onagraceae)." Evolution 24:578-579.

U.S. Fish and Wildlife Service. 1978. "Determination of Antioch Dunes evening-primrose, Oenothera deltoides ssp. howellii, as an Endangered Species." Federal Register 43: 17916.