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NATURAL HISTORY

THREAD-LEAVED BRODIAEA } Brodiaea filifolia
FAMILY: Liliaceae

DESCRIPTION: This shy, perennial herb grows to be anywhere from eight to 16 inches tall and is visible aboveground only in the spring of good rainfall years. For most of the year, the plant is composed solely of its underground bulb and remnants of an underground stalk. During flowering season, each plant puts out its thread-like leaves and blooms with several pale purple flowers, from one to 1.3 centimeters long, arranged in a loose umbel. The slender, pale green flower stalks bear one to six narrow, scythe-shaped leaves. This plant is distinguishable from other Brodiaea species by its thin, pointed stamen. Later in the breeding season, it bears capsulate fruit, which split to release their seeds.

HABITAT: The thread-leaved brodiaea prefers open ground such as floodplains, grasslands, and gentle hillsides, particularly near vernal pools. It is usually found at an altitude between 100 and 2,500 feet above sea level, in clay or semi-sandy soils.

RANGE: The thread-leaved brodiaea is found in Los Angeles, San Bernardino, Riverside, San Diego, and Orange counties in California.

LIFE CYCLE: The thread-leaved brodiaea germinates from an underground corm, or type of bulb, and can only be detected aboveground during its short flowering season in May and June. Thread-leaved brodiaea are self-incompatible, which means that in order to reproduce, a plant must have pollen from another, genetically distinct plant. Though many insects may visit a flower, only two types of insect — the tumbling flower beetle and the sweat bee — are known to pollinate the thread-leaved brodiaea effectively. Once a plant has been pollinated and its seeds have matured, the fruit splits, releasing many tiny black seeds to be scattered nearby. Of the seeds that are dispersed, only a small percentage will make it to maturity. The success of the thread-leaved brodiaea’s breeding depends on the annual precipitation, as well as the populations of other plants in the area. Once the breeding season is over and the weather starts to dry, the plants die back down to an underground remnant stem filled with stored nutrients so that it may survive adverse weather. Plants remain there for the rest of the year, rising again only to bloom in the spring.

THREATS: The thread-leaved brodiaea is in danger from expanding urban development, habitat fragmentation, human alterations of water regimes, damage by livestock and off-road vehicles, clearing for firebreaks, weed control measures, manure and sewage dumping, and competition from nonnative plant species.

POPULATION TREND: Gathering data on thread-leaved brodiaea populations can be quite difficult, as the plant is only above ground for a few months every year. The Carlsbad Fish & Wildlife Office lists 84 populations, while the California Department of Fish and Game lists 25 to 30. All sources seem to agree, however, that populations are in decline. According to the West Riverside County Multiple Species Habitat Conservation Plan, more than half of thread-leaved brodiaea populations contain fewer than 500 individuals; o nly six of these populations contain more than 5,000 plants. Key populations of remaining plants are concentrated on the Santa Rosa plateau and along the San Jacinto River.

Photo by David Bramlet