Peirson's Milk Vetch (Astragalus magdalenae Greene var. peirsonii (Munz & McBurn) Barneby]
Listing CNPS List 1B R-E-D Code 2-2-2
State/Federal. Status -- CE/PE FABACEAE Dec.-Apr.
Global Rank G3G4T2 State Rank S2.2
Distribution: San Diego County, Imperial County; Arizona; Baja California and Sonora, Mexico
Habitat: Well developed desert dunes are the preferred habitat of this short-lived perennial. The dearth of this habitat on the San Diego County deserts probably accounts for its rarity there. Much better habitat is found on the dune systems east of El Centro in Imperial County.
Known Sites: No recent sightings in San Diego County are known. A single unconfirmed collection is reported from dunes near Borrego Spring; it is to be searched for during years of good desert rains. The nearest known extant locale is the Algodones Dunes in Imperial County (e.g., 4 miles west of Glamis; 9.6 miles east of the Highland Canal; 22 miles east of Brawley; east of Holtville) where this species is localized following years of good rainfall. Biological survey reports note a site approximately 8 miles north of the Superstition Hills, as well as north of the New Coachella Canal and north of Highway 78. Shreve and Wiggins report this species in Arizona from the vicinity of Yuma.
Growing southeast to Puerto Penasco in Sonora; the variety peirsonii has a primarily eastern range from San Diego County. Astragalus magdalenae var. magdalenae has 15 collections from Baja California in the San Diego Natural History Museum's herbarium; south to Santa Maria Bay at 24 46' North where collected by Moran (SD 50266); it also has been collected on Natividad Island.
Status: This species is presumed stable in the southern deserts. The status of Peirson's Milk Vetch in San Diego County is unknown. Until more cumulative population and range information is available, all populations should be protected.
Copyright © May 1994 Craig H. Reiser.