Scientific: Vachellia farnesiana (formerly Acacia farnesiana) and Vachellia farnesiana var. farnesiana (formerly Acacia smallii).
Common: huisache, sweet acacia
Family: Fabaceae
Origin: Altiplano highlands of central Mexico north of Mexico City north to the Big Bend area of south Texas. Naturalized and cultivated as an agricultural and ornamental tree all over the world in warm, arid climates, e.g. Africa and Australia. Huisache has naturalized throughout Indian subcontinent.

Pronounciation: Va-KEL-lee-a far-nes-ee-A-na

Hardiness zones
Sunset
8, 9, 12-24
USDA 8-10 (arid zones only)

Landscape Use: Small accent tree for both color and smell; both species make an ideal multiple trunk tree for small spaces where a little debris is tolerated primarily in xeric landscape as a large background shrub or small tree. In the Phoenix area, sweet acacia should not to be used as a median tree where extensive crown manipulation is required because of the high sensitivity to trunk sunscald injury.

Form & Character: Evergreen to deciduous or semi-deciduous, naturally multi-trunk or trained into standard form, growth to 30 feet in height with near or equal spread, rounded, stiff and open to lacey and airy, xeric.

Growth Habit: Slow to moderate to 15 to 35 feet with equal spread depending on whether V. farnesiana var. farnesiana (taller, but highly variable) or V. farnesiana (usually smaller). Here is a comparative image showing as relatively young and immature street median trees (a poor landscape use by the way) both V. farnesiana (left) and V. farnesiana var. farnesiana (right).

Foliage/texture: Small twice pinnately compound green to gray-green foliage, stems and trunk, brown and well armed with 1 inch white, stipular spines underneath foliage that break off in skin and infect, fine texture. Note that V. farnesiana is slightly coarser textured than the variety farnesiana because of it's often stiffer habit and smaller size.

Flowers & fruits: Small orange powder puff flowers on mostly old wood, highly fragrant, fruit a 1 to 3 inch dark brown pod.

Allergy alert: Some people are allergic to the the pollen from sweet acacia flowers.

Seasonal color: Yellow to sulfur yellow in late November to March. Varies slightly year to year depending on winter cold. The flower fragrance of sweet acacia can be smelled throughout the Phoenix metropolitan area in early spring.

Temperature: Hardy to 15o to 25oF.

Light: Full sun, absolutely NO shade.

Soil: Tolerant of alkalinity.

Watering: Little to no supplemental irrigation once established. However, grows much larger if irrigated.

Pruning: Huisache has a tendency to sprout epicormic shoots or suckers at ground level and at large pruning cuts or wound sites, elsewise prune to desired shape. Caution though, if the canopy base of A. farnesiana is raised to high exposing the trunk to western sun, then the trunk will scald. Wear gloves and a long sleeve shirt or else you will itch and fester!

Propagation: Seed, must acid scarify, 95% sulfuric acid for 30 minutes or until dark seed coat initially lightens.

Disease and pests: Texas root rot

Additional comments: The form and size of V. farnesiana and it's variety farnesiana are similar, yet discernable differences do exist as shown in the image above. V. farnesiana is generally smaller, slower growing, flowers about a month earlier, is slightly less cold hardy, and might be less susceptible to Texas root rot than the variety farnesiana. Whether your druthers are to differentiate between the species and it's variety is elective. In any regard huisache is a wonderful, small accent tree if not over irrigated! V. farnesiana var. minuta has a very restricted range in arroyos of Baja California, where it is sympatric with V. farnesiana var. farnesiana.

Ethnobotany notes: Huisache perfume is distilled from it's flowers. Huisache flowers are employed in preparation of violet bouquets, extensively used in European perfumery. Sweet acacia pomades are manufactured in Uttar Pradesh and the Punjab of India. Seed pods of huisache contain 23% tannin, a glucoside of ellagic acid, and are used for tanning leather. Sweet acacia bark is also used for tanning and dying leather in combination with iron ores and salts. In Bengal and West Indies, seed pods are used for a black leather dye. A gummy substance obtained from seed pods is used in Java as cement for broken crockery. Gum exuding from the trunk is considered superior to gum arabic in the arts. Huisache trees are used as an ingredient for arrow poison in the Ivory Coast of Africa; elsewhere they are used as fences and to check erosion. The wood of huisache is hard and durable underground. It is used for wooden plows and for pegs and the seeds, contain an unnamed alkaloid, and reportedly has been used to kill rabid dogs in Brazil.