[Illustration: Astragalus mollissimus]
Common names: MILKVETCH, LOCOWEED, RATTLEWEED, WOOLLY-LOCO
Arizona and California deserts: (_Astragalus nuttalianus_).
White-purple. February-May.
Texas deserts: (_Astragalus mollissimus_). Purple. April-May.
Pea family. Size: 4 to 12 inches high.
A very large genus of plants, with 78 species recorded in Arizona alone,
_Astragalus_ ranges from the driest, hottest parts of the desert to high
mountain peaks and the far north. _A. nuttalianus_ is the commonest of
the desert species and is found on dry plains, mesas, and slopes below
4,000 feet from Arkansas and Texas westward to California and south into
Mexico.
Some of the species, of which _Mollisimus_ (Wooly-loco) is one, contain
a poisonous constituent causing the well-known and often fatal loco
disease of livestock, particularly horses. (Loco is a Spanish word
meaning “crazy.”) Other species which prefer soils rich in selenium take
up enough of that toxic mineral to make them poisonous to livestock,
especially sheep.
Nearly all of the species are colorful and spectacular when in blossom,
and some of them have a rank, disagreeable odor.