Desert Rock Pea
Shrubby Deer Vetch

Acmispon (Lotus) rigidus

Acmispon (Lotus) rigidus Watercolor © by Michael Plagens

Watercolor illustration from a specimen found in flower and fruit at Superstition Mts., Pinal Co., Arizona. 29 Feb. 1992. Desert Rock Pea provides important forage for Desert Bighorn Sheep (Ovis canadensis).

PERENNIAL: The herbaceous growth reaches a height of 50± cm from a slightly woody crown. The twigs are succulent and brittle.

Yellow Pea flower of Acmispon (Lotus) rigidus Acmispon rigidus seed bean pod © by Michael Plagens
FLOWERS: This perennial produces lush growth and abundant yellow-orange pea flowers very early in the spring (Jan-Apr).

RANGE:In spring, Desert Rock Pea can be found on rocky slopes nearly throughout the Arizona Sonoran Desert. Also known as deer vetch, it is important forage for Desert Mule Deer and Bighorn Sheep.

LEAVES: Compound leaves have 3-5 leaflets.

FRUIT: The pods take on a bright reddish hue as they mature. As they dry further the two halves of the pod (valves) begin twisting in opposite direction but are held in place by the seam holding them together. When the force finally breaks the valves spring and twist open suddenly ejecting the seeds far from the parent plant.


Acmispon rigidus seed bean pod © by Michael Plagens

Cool moist winters favor an abundance of Pea Aphids on desert rock pea which attract many Convergent Lady Beetles (Hippodamia convergens) whose larvae devour the aphids.

Fabaceae -- Bean Family

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More Information:

Sonoran Desert Field Guide
Sonoran Desert Places
Sonoran Desert Naturalist Home Page


Copyright Michael J. Plagens, page created 16 Nov. 2005,
Updated 24 Dec. 2019.