Descanso Milk Vetch [Astragalus oocarpus Gray]

Descanso Milk Vetch [Astragalus oocarpus Gray]

Listing CNPS List 1B R-E-D Code 3-2-3

State/Federal. Status -- /C2 FABACEAE May-Aug.

Global Rank G2 State Rank S2.2

Distribution: San Diego County

Habitat: Cismontane chaparral edges at the periphery of meadows is a typical habitat for the Descanso Milk Vetch. Most locales observed have species of Arctostaphylos and other woody shrubs well interspersed with Adenostoma fasciculatum. Crouch coarse sandy loams are utilized at Jeff Valley. As with many other Astragalus, mild soil disturbance may be a factor in facilitating the spread of populations.

Known Sites: This species is easily confused when not in fruit with Astragalus douglasii. Descanso Milk Vetch has very distinctive, short pods. Scattered locales from Palomar to Cuyamaca Mountains include herbarium collections from 1.5 miles east of Santa Ysabel, Black Canyon 1 mile south of Mesa Grande, and at the San Diego River Falls. This plant may be either under or over-reported due to confusion with A. douglasii. It is definitely not common as is sometimes suggested; it grows along the road near the approach to Volcan Mountain, along trails east of Green Valley Campground, and is locally plentiful alongside trails in Jeff Valley on Palomar Mountain. Reports are from Echo Valley, Ballena, the Lake Henshaw area, and in the eastern San Pasqual Valley. Herbarium specimens examined are from Descanso near Central Avenue, Boulder Creek Road, Julian, the Cedar Creek Falls on the San Diego River, Witch Creek, Black Canyon 1 mile south of Mesa Grande, Pine Hills, Carrizo Creek near Lake Henshaw, and on the Wyss Ranch in the Palomar Mountains. Old biological survey reports are from the Hosking Ranch near Wynola, as well as 0.25 mile east southeast of Aguanga near Highway 79. Data Base Reports are along Oak Grove Drive in Descanso, 1.5 miles east of Santa Ysabel near Highway 78, 5 miles north of Santa Ysabel, and on the south side of Airplane Ridge just north of Arroyo Seco in the Cuyamaca Mountains.

No collections from Baja were found in the San Diego Natural History Museum's herbarium.

Status: Montane populations of the Descanso Milk Vetch, a San Diego County endemic, are presumed stable. Continued recreational use of the Cuyamaca Mountains, including activities such as horse riding and mountain bikes, could negatively impact this species. While this Astragalus may actually increase in numbers where soils are mildly disturbed, heavy horse or bike traffic could reverse such a trend. All substantial populations should be protected.

Copyright May 1994 Craig H. Reiser.

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