Munz's Onion

Allium munzii

Description

Munz's onion (Allium munzii ), a member of the lily family, is a perennial herb, 0.5-1.2 ft (15.2-36.6 cm) tall, originating from a bulb with a papery, reddish-brown outer coat and light brown inner coat. The single leaf is cylindrical in shape and up to 1.5 times as long as the stalk of the inflorescence (flower cluster), which is umbrella-shaped with 10-35 flowers. The flowers have six undifferentiated petals and sepals that are white, or white with a red midvein, becoming red with age. They are 0.2-0.3 in (5.1-7.6 mm) long. The ovary is crested with fine, irregularly pointed processes, and the fruit is a three-lobed capsule.

Munz's onion can be distinguished from other members of the genus within its range by its solitary cylindric leaves, elliptic to ovate perianth segments, generally white flowers, and finely and irregularly dentate ovary crests.

A. munzii was first referred to as A. fimbriatum var. munzii. In 1992 it was elevated to species status.

Habitat

Munz's onion is restricted to mesic clay soils in western Riverside County, California. It is frequently found in association with southern needle-grass grassland, mixed grassland, and grassy openings in coastal sage scrub or, occasionally, in cismontane juniper woodlands.

Distribution

Little is known about the historical distribution of Munz's onion. However, as much as 80-90% of the clay soils in western Riverside County that may have supported habitat for Munz's onion have been adversely modified through extensive agriculture, urbanization, and clay mining.

Munz's onion is known from 13 extant populations. There are an estimated 20,000-70,000 individuals of this species. In response to rainfall and other factors, perennial bulbs may not produce aerial leaves or flowers in a given year or may produce only leaves. As a result, fluctuations in numbers of observed individuals can be misleading. Five populations are large (more than 2,000 individuals) and cover as much as 20 acres (8 hectares). Most populations contain fewer than 1,000 individuals, and their areas range from several square yards to 2.5 acres (1 hectare).

Threats

Munz's onion was extirpated in the 1990s from at least two sites as a result of agricultural development, clay mining, and highway construction. Other populations of this species have been impacted by a reduction of available habitat and numbers of individuals. One population of Munz's onion was partially eliminated in 1982 by the re-alignment of the Interstate 15 freeway corridor in the Temescal Valley of Riverside County. Another population was reduced when part of its habitat was inundated for a reservoir.

Two of the remaining 13 populations of Munz's onion are within the boundaries of proposed development. Discing (plowing) for weed abatement or dryland farming may destroy habitat and cause population declines. One site that has been persistently disced for dryland farming since 1992 has suffered a staggering loss, going from 1,000 individuals that year to fewer than 10 individuals in 1998. Seven of the 13 populations supporting about 20% of the individuals are threatened by loss of habitat through development, discing, and off-road vehicle activity.

Non-native grass species such as Avena barbata and Bromus madritensis are dominant on the clay soils required by Munz's onion. Crowding and competition for resources from these grasses threaten the majority of the 13 occurrences of Munz's onion.

Conservation and Recovery

The California Fish and Game Commission has listed Munz's onion as threatened under the Native Plant Protection Act and California Endangered Species Act. Although both statutes prohibit the take of state-listed plants, populations have continued to decline. For example, development proposals in Carlsbad (San Diego County) and in the Gavilan Hills (Riverside County) that involve direct impacts to Munz's onion have proceeded without notification to the wildlife agencies.

Contact

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

Reference

U. S. Fish and Wildlife Service. 13 October 1998. "Determination of Endangered or Threatened Status for Four Southwestern California Plants from Vernal Wetlands and Clay Soils." Federal Register 63 (197): 54975-54994.