Regularity: Regularly occurring
Localities documented in Tropicos sources
United States (North America)
Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.
- Anonymous. 1986. List-Based Rec., Soil Conserv. Serv., U.S.D.A. Database of the U.S.D.A., Beltsville. http://www.tropicos.org/Reference/1103
- Williams, M. C. & R. C. Barneby. 1977. The Occurrence of Nitro-toxins in North America Astragalus (Fabaceae). Brittonia 29(3): 310–326. http://www.tropicos.org/Reference/94
- Munz, P. A. & D. D. Keck. 1959. Cal. Fl. 1–1681. University of California Press, Berkeley. http://www.tropicos.org/Reference/1717
- Barneby, R. C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(1–2): 1–1188. http://www.tropicos.org/Reference/85
- Berg, K. & R. Bittman. 1988. Rediscovery of the Humboldt Milk-vetch. Fremontia 16(1): 13–14. http://www.tropicos.org/Reference/10617
Global Range: Though primarily known from Mendocino County, there are a few occurrences in Humboldt Co., CA. The main cluster of populations in Mendocino Co. cover about 450 sq mi. There are disjunct populations in Humboldt Co. and including those makes the range extent closer to 1700 sq mi.
Comments: Logged mixed evergreen forest; appears to need open areas.
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 21 - 80
Comments: Once thought to be extinct, this plant was rediscovered in 1987. By 2005, many populations had been located, mostly by foresters surveying pre-timber harvest areas. About 50 occurrences known in 2005.
National NatureServe Conservation Status
Rounded National Status Rank: N2 - Imperiled
NatureServe Conservation Status
Rounded Global Status Rank: G2 - Imperiled
Reasons: Previously not seen since 1954, Astragalus agnicidus was rediscovered in 1987. As of 2005, it is known only from two counties in California and about 50 occurrences. Many new populations have been found, but few are ranked "good" or better. Many plants are reported, though numbers are somewhat in question and their long-term viability is unknown. Astragalus agnicidus occurs in forested areas where the canopy has recently been opened. It is threatened by logging treatments such as herbicide application.
Environmental Specificity: Moderate. Generalist or community with some key requirements scarce.
Comments: Occurs in forested areas in Mendocino and Humboldt counties where canopy has recently been opened.
Global Short Term Trend: Relatively stable to decline of 30%
Comments: Though many populations are located during pre-project surveys and will be disrupted to some extent, this plant does respond positively to disturbance and actually requires openings to germinate. Short term trend is therefore stable to slightly declining. The decline associated with timber harvest is probably due more to herbicide use than to the actual harvest.
Global Long Term Trend: Increase of 10-25% to decline of 30%
Comments: Long term trend is estimated to be relatively stable.
Degree of Threat: Medium
Comments: This species is threatened by grazing and certain logging treatments such as herbicide use. Other threats include encroachment of non-native plants and road maintenance.
Astragalus agnicidus is a rare species of milkvetch known by the common name Humboldt County milkvetch. It is endemic to northern California, where it is known only from two populations in Humboldt County and one in Mendocino County.
The plant was undescribed until the 1950s. Until then it was known only from one 8-acre (32,000 m2) ranch in Humboldt County, where sheep ranchers blamed the unnamed species for the deaths of their animals, which may have eaten it. They eradicated the plant from their land, and by the time it was formally described and named in 1957 it was thought to be extinct. The species name given the plant, agnicidus, means "lamb-killer".
The plant was rediscovered in 1987. A few individuals were found growing in a recently bulldozed clearing, their long-buried seeds having been plowed into favorable conditions for germination. The plants were brought under the protection of the landowners, the same family that was responsible for its near-extinction and had changed their minds about its value. Two other populations of the plant have since been discovered in areas of the coastal mountains that had been recently logged; this is an early successional species which arises in disturbed areas. Too much disturbance of an area can be harmful, however, since it may cause the whole patch of buried seeds to sprout at once, making the population vulnerable to destruction as it lacks backup seed stores.
This milkvetch is a perennial herb which lives 5 to 10 years. The coarse reddish stem is slightly hairy toward the ends, growing 30 to 90 centimeters long. The widely spaced leaves are arranged oppositely along the stem. Each is up to 16 centimeters long and is made up of several pairs of oval-shaped leaflets up to about 2 centimeters long. The inflorescence is a dense cluster of 10 to 40 white pealike flowers. The plant is self-pollinating and the flowers are also pollinated by native bumblebees. The fruit is a bent legume capsule 1 to 1.5 centimeters long which dries to a papery texture.
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