Endangered Species Recovery Program

11. Merced Monardella (Monardella leucocephala)

• Taxonomy
• Description
• Historical and Current Distribution
• Life History and Habitat
• Reasons for Decline and Threats to Survival
• Conservation Efforts
• Conservation Strategy

Taxonomy.-- Merced monardella is known today by the scientific name published by Gray (1867), Monardella leucocephala. The type specimen was collected in Merced County on the plains near the Merced River (Epling 1925). Greene transferred Merced monardella to the genus Madronella in 1906, but Epling (1925) returned the species to Monardella. The scientific name has not been altered since (Jokerst 1993, Stebbins 1993). Merced monardella is a member of the mint family (Lamiaceae).

Description.-- Merced monardella (Figure 32) has square stems 15 to 20 centimeters (6 to 8 inches) tall. Both the stems and the opposite, lance-shaped leaves are gray-hairy and have a characteristic mint scent. Although the white flowers are tiny, the flower heads are showy because each one is surrounded by a circle of white bracts. Merced monardella can be distinguished from the related species Sierra monardella (M. candicans) and coyote-mint (M. villosa) by the color of the stems, bracts, and flowers; microscopic differences in the flowers; and habitat (Munz and Keck 1959, Jokerst 1993).

Figure 32. Illustration of Merced monardella.

Historical and Current Distribution.-- Historically, Merced monardella was collected from five individual sites that were clustered in two areas: (1) near the Merced River south of Delhi in Merced County (including the type locality); and (2) along the Tuolumne River near La Grange and Waterford in Stanislaus County (Figure 33). The most recent record of the species was from 1941 (Skinner and Pavlik 1994, CDFG 1995, Stebbins 1993). Merced monardella was not found at historical sites during surveys from 1990 through 1992, but may persist on private lands where access was denied (Stebbins 1993).

Figure 33. Distribution of Merced monardella (Monardella leucocephala).

Life History and Habitat.-- This annual plant may grow only in years of above-average precipitation; it flowers in May, June, and July after the soil dries. Merced monardella is restricted to extremely sandy, subalkaline soils in low-lying areas bordering rivers. The native vegetation in these areas is grassland, but several collections were made in dry-farmed fields. The only associated species mentioned by collectors was naked buckwheat (Eriogonum nudum). Elevations at the historical sites range from approximately 15 to 80 meters (50 to 260 feet) (Hoover 1937, CDFG 1995, California Native Plant Society 1988b, Stebbins 1993).

Reasons for Decline and Threats to Survival.-- Much of the suitable habitat for Merced monardella was converted to agriculture more than 50 years ago (Hoover 1937). The intensive, irrigated agriculture practiced today is incompatible wih survival of this species, unlike the dry-land grain farming common in the past. Other activities that may have contributed to its decline include urban development and sand and gold extraction. The remaining suitable habitats that may support undiscovered populations are primarily in private ownership and thus are subject to these same threats (CDFG 1995, California Native Plant Society 1988b, Stebbins 1993).

Conservation Efforts.-- USFWS sponsored a status survey for Merced monardella, which included field surveys from 1990 through 1992. California Native Plant Society has stressed the importance of conducting surveys for Merced monardella, although this species has been listed as "presumed extinct" pending rediscovery (Skinner and Pavlik 1994, Skinner et al. 1995).

Conservation Strategy.-- To ensure long-term conservation of Merced monardella, the strategy is to protect at least five distinct populations. Protected areas should be natural land in blocks of at least 65 hectares (160 acres) and should contain a minimum of 1,000 individuals to reduce the likelihood of extinction from intrinsic or random processes. Surveys for Merced monardella must be continued in both historical sites and suitable habitats, especially in years of above-average precipitation. The cooperation of private landowners is a prerequisite for surveys at some sites, and therefore an incentive program should be devised. If any populations are found, site-specific threats must be determined and negated. Monitoring should be initiated in all populations if the species is rediscovered. The status of Merced monardella should be reevaluated within 5 years of recovery plan approval or when surveys have been completed, whichever is less.