Koeberlinia spinosa, allthorn

Uncommon shrub in Sonora and Arizona, but can grow in thickets where it does occur. As the name implies it is "all thorns" with unnoticeable leaves and small flowers. It grows primarily in the Sonoran Desert, semi-desert grasslands and into the Chihuhuan Desert. Often it will creep along the ground in a low, impenetrable thicket, but can sometimes ascend and become large and tree-like.