The Algodones Dunes are home to several rare, threatened or endangered plant species. A member of the bean and pea family, it can grow to 2.5 feet tall and is notable among milkvetches for its greatly reduced leaves. Peirson s Milkvetch produces attractive, small purple flowers, generally in March or April, on stalks with 10 to 17 flowers per stalk. It yields inflated fruit similar to yellow-green pea pods with triangular beaks. Peirson s milk vetch has the largest seeds of any Milkvetch.
Large seeds are an important adaptation in dune plants.
While small seeds can readily germinate under several inches of moist sand, they may exhaust their stored food before the seeding can emerge from the sand at such depths and begin producing its own food. Peirson s Milkvetch is named for Frank Peirson, an early California plant collector who was the first to prepare a scientific collection of the plant back in 1927. In the United States, the plant is known only from the Algodones Dunes, and in nearby Mexico from a limited area of dunes within the southern Gran Desierto, in the northwestern portion of the state of Sonora. This silver-leafed member of the sunflower, or aster, family inhabits primarily the interior portions of the dunes at the bases along the sides of large dunes. Extremely tolerant of moving sand, it grows rapidly to avoid being buried.