Acmispon maritimus is a species of legume known by the common name coastal bird's-foot trefoil. It is native to the southwestern United States and northern Mexico, where it grows in many types of mountain, desert, and scrub habitat, not necessarily near the coast. It is an annual herb quite variable in morphology, from petite to bushy, hairless to roughly hairy, and prostrate to erect in form. The slender stems are lined with leaves each made up of pairs of leaflets variable in shape and size. The flower cluster is a small array of 1 to 4 yellow flowers, each up to a centimeter long or so. The elongated flower corolla emerges from a tubular calyx of sepals. The fruit is a fairly straight legume up to 3 centimeters long. Laboratory studies have shown this species, which occurs in wildfire-prone habitat such as chaparral, to have an increased rate of seed germination after exposure to heat.