An Illustrated Guide to ARIZONA WEEDS
The University of Arizona Press
WHITETHORN, mescat acacia
WHITETHORN-Acacia constricta Benth. and var. vernicosa (Standl.) Benson
DESCRIPTION-Whitethorn is a tall shrub up to 10 feet high, mostly armed with slender straight white spines in pairs, 1/4 to 1 1/2 inches long. Some limbs are spineless, or often entire plants may be spineless. The leaves are twice divided, first into 3 to 7 (or sometimes only 1 or 2) pairs of main divisions, and are further divided into 5 to 16 pairs of tiny secondary leaflets.
The small fragrant golden yellow flowers are clustered into many flowered conspicuous balls on long stalks arising from the leaf axils. They derive their color principally from the many (30 to 40 on each flower) stamens, which are much longer than the 5 tiny yellow petals. The reddish brown curved pods, 2 1/2 to 5 inches long, are about 1/8 inch broad and indented, or constricted between each seed. The boatshaped smooth seeds, about 1/4 inch long and 1/12 inch broad, are mottled dark brown, gray, and black.
In southeastern Arizona, the twigs, leaves, and pods of many plants are very glandular and sticky. These are chihuahua whitethorn or stickyleaf whitethorn (Acacia constricta var. vernicosa).
DISTRIBUTION-Abundant in rocky caliche or limestone soil along washes, slopes, and mesas throughout the deserts and desert grasslands of southern Arizona. It also occurs in central Arizona in the lower chaparral, desert grassland, and desert shrub associations; 2,000 to 5,000 (rarely 6,250) feet elevation; flowering May to November, mostly May to July.
Although browsed to some extent, whitethorn has little forage value, and has become a range pest in some areas because of its encroachment on grasslands, as in Cochise County.
POISONOUS PROPERTIES-Whitethorn, like Johnsongrass, produces hydrocyanic acid under certain conditions.
Copyright (c) 1972 The Arizona Board of Regents