Few-flowered Navarretia

Navarretia leucocephala ssp. pauciflora

Description

Few-flowered navarretia, Navarretia leucocephala ssp. pauciflora is a low-growing, spreading, and much-branched annual herb in the phlox family (Polemoniaceae). This plant grows to a height of 0.4-1.6 in (1-4 cm). The nearly hairless leaves are linear and entire, or parted into a few linear lobes, and 0.4-1.0 in (1-2.5 cm) long. The inflorescence is a head of 2-15 blue or white (fading to blue) flowers. A few spiny, leaf-like bracts below each head extend out 1.5 to 3 times the radius of the head; bracts within the head are shorter. The funnel-shaped corollas are 0.2-0.3 in (5-7.5 mm) long with five lobes 0.06 in (1.5 mm) long. Each corolla lobe has a single unbranched vein. The stigma has two minute lobes. Few-flowered navarretia flowers from May to June.

Five subspecies of N. leucocephala are currently recognized, two of which may hybridize with N. leucocephala ssp. pauciflora. These two subspecies, N. leucocephala ssp. bakeri and N. leucocephala ssp. plieantha, differ from N. leucocephala ssp. pauciflora in stature; degree of hairiness; and size, number, or lobing of floral parts. The flower color in ssp. plieantha also differs, being bright blue rather that white or pale blue as in ssp. pauciflora. The U.S. Fish and Wildlife Service has had a pending proposed policy since February 1996 on the treatment of intercrosses and intercross progeny that says "intercross progeny" (hybrids) that are the result of a cross involving a listed taxon receive protection under the Act if the progeny more closely resemble the listed parent's taxon. This policy, if finalized, will primarily apply to a population at Loch Lomond, which is a product of intercross between ssp. plieantha and ssp. pauciflora. This hybridized Loch Lomond population of N. leucoephala would then be treated as if it were listed because both parental taxa will be listed with the publication of this rule. The intercross policy could also apply to two historical populations in Sonoma County. Day identified herbaria specimens of these populations in 1993 as intermediates between ssp. plieantha and ssp. bakeri (a non-listed taxon). However, at least one of these populations appears to be no longer extant. Should these populations be rediscovered, a morphological assessment would be required to determine the applicability of any intercross policy and subsequent protection under the Act.

The type specimen for N. pauciflora was collected in 1946 from a playa 5 mi (8 km) north of Lower Lake, Lake County, California. The treatment of Navarretia was revised in 1993, reducing N. pauci-flora to a subspecies of N. leucocephala. More than a dozen species of Navarretia occur in the region, including several restricted to vernal pools. Both N. leucocephala ssp. pauciflora and N. leucocephala ssp. plieantha are restricted to northern ash-flow volcanic vernal pools, a pool type with a very limited distribution.

Habitat

Few-flowered navarretia is found growing in volcanic ash substrate, clay pan vernal pools in chaparral, grassland, or mixed coniferous forest in southern Lake and Napa Counties.

Distribution

The subspecies occurs over a 20 sq mi (52 sq km) area at elevations of 1,400-2,800 ft (420-840). Historically, N. leucocephala ssp. pauciflora was known from nine sites in Napa and Lake counties. The subspecies has become extirpated from six historical localities. Two new localities were found in 1989. The five extant populations occur on private lands.

Threats

Few-flowered navarretia is endangered because of the vulnerability of its restricted habitat to threats posed by urbanization, agricultural land conversion, drainage, vernal pool and pond construction, ditch construction, off-highway vehicle use, road maintenance, and random natural events.

One population of few-flowered navarretia has been adversely affected by drainage, and one population has been adversely affected by an attempt to create a more permanent water source. The Manning Flat site in Lake County has significantly eroded as a result of excavation of drainage ditches; this erosion has reduced the population and the habitat. This population is also within the right-of-way of State Route 29, and there is substantial concern that individual plants may be damaged by highway maintenance. The intercross population of N. leucocephala ssp. plieantha with N. leucocephala ssp. pauciflora at Loch Lomond is adjacent to State Route 175, where maintenance activities could result in the loss of plants. Off-highway vehicle use has damaged several population sites in Lake County. Conversion of land to a rice field adversely affected another Lake County population of this plant. Construction of a stock pond for cattle partially destroyed the population of N. leucocephala ssp. pauciflora at Ely Flat in Lake County and severely altered the hydrology of its habitat. Agricultural land conversion threatens this same population. Although the intercross population at Loch Lomon cited above occurs in an ecological reserve managed by the California Department of Fish and Game, the site is potentially threatened by timber harvesting within the watershed. This vernal pool and its flora could be markedly degraded by such activity. Eighty percent of one population of this taxon in Napa County was adversely affected by the rooting of feral pigs, while horse grazing threatens two other populations and cattle grazing threatens one other population.

Conservation and Recovery

Conservation of the few-flowered navarretia requires the protection of its critical habitat of ash-flow volcanic vernal pools. Only five of these critical habitats survive. All are on private lands and are potentially threatened by various human influences. These habitats should be protected by acquiring the land and designating ecological reserves, or by negotiating conservation easements with the owners. The populations of the few-flowered navarretia should be monitored, and research undertaken into its biology, habitat needs, and beneficial management practices. A program of public education should be developed to inform local people of the important of protecting vernal pools and their rare plants.

Contacts

U.S. Fish and Wildlife Service
Sacramento Fish and Wildlife Office
Federal Building
2800 Cottage Way, Room W-2605
Sacramento, California 95825-1846
Telephone: (916) 414-6600
Fax: (916) 460-4619

U. S. Fish and Wildlife Service
Office of the Regional Director
Eastside Federal Complex
911 N.E. 11th Avenue
Portland, Oregon 97232-4181
Telephone: (503) 231-6118
Fax: (503) 231-2122

Reference

U.S. Fish and Wildlife Service. 18 June 1997. "Endangered and Threatened Wildlife and Plants; Endangered Status for Four Plants From Vernal Pools and Mesic Areas in Northern California." Federal Register 62 (117): 33029-33038.