Fouquieria columnaris, the Boojum tree or cirio (American Spanish: [ˈsiɾjo]) is a tree in the ocotillo family,(Fouquieriaceae) whose other members include the ocotillos. Some taxonomists place it in the separate genus Idria. It is nearly endemic to the Baja California Peninsula (both the northern and southern states), with only a small population in the Sierra Bacha of Sonora, Mexico. The plant's English name, Boojum, was given by Godfrey Sykes of the Desert Laboratory in Tucson, Arizona and is taken from Lewis Carroll's poem "The Hunting of the Snark".
This plant is a columniform, upwardly tapering tree. The central axis of the plant is homologous to the single stem of other species. It has a cortical water-storage network, a feature unique to the family.
The Fouquieria columnaris trunk is up to 24 inches (61 centimeters) thick, off-white in color, with few or no major branches and with numerous thin, twiggy branches sticking out at right angles, all covered with small leaves 1.5–4 cm (0.59–1.57 in) long. They can grow to a height of 20 meters (almost 70 feet), but the tallest, in Montevideo Valley between Mission San Borja and Bahia de los Angeles is 86.5 feet (26.4 meters) in height,the second tallest succulent after Euphorbia ampliphylla.
The flowers bloom in August and September regardless of rainfall; they occur in short racemes, and have a honey scent. The flowers have short, cream-yellow corollas, with the limb of the petals inflexing around the filaments of the stamens. The anthers and stamens protrude out, while the stigma is protected by the inflexed petal limbs. The flowers are visited by at least 15 species of bees in 11 genera, who pry open the inflexed corolla limbs to obtain the sweetened nectar and contact the protected stigma.