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Vachellia spp.

thorn trees

Fabaceae

Africa, with species across the Americas, Asia, and Australia

Attracts Pollinators Attracts Butterflies Deer Resistant Drought Tolerant Fragrant (moderate)

SunFull Sun

WaterLow · drought-tolerant

Overview

Vachellia spp. is a genus of roughly 160 species of trees and shrubs in the legume family (Fabaceae), separated from Acacia spp. in the broad sense and including many of the thorn trees of Africa. Plants range from low shrubs about 3 feet (1 m) tall to spreading trees reaching 98 feet (30 m), most with flat or rounded crowns held on a short trunk. The bipinnate leaves are divided into many small leaflets, and paired stipular spines, sometimes swollen and hollow, guard the twigs. Flowers are massed into rounded heads or short spikes 0.3–0.6 inch (8–15 mm) wide, yellow to cream, and scented; they are followed by flattened or coiled pods 2–8 inches (5–20 cm) long. The genus is centered in Africa but extends across the Americas, Asia, and Australia in savanna, dry woodland, and semi-desert. Deep root systems and drought tolerance suit plants to seasonally dry climates, though most species are damaged by hard frost. Several species form swollen-thorn associations with ants that occupy the hollow spines. The wood, bark, and pods are used for fodder, gum, and timber across the range.

Native Range

The genus is centered in Africa, where most thorn-tree species occur in savanna and dry woodland. Additional species are native to the Americas, southern Asia, and Australia. Vachellia spp. grows in semi-arid grassland, scrub, and seasonally dry forest, generally on free-draining soils.

Suggested Uses

Vachellia spp. is planted for shade, windbreaks, and erosion control in dry-climate landscapes, spaced well apart to allow the spreading crown to develop. Several species are grown for fodder, gum arabic, and nitrogen fixation in agroforestry. The flowers support bees and the seeds and foliage feed browsing wildlife.

How to Identify

Twigs carry paired stipular spines at the leaf bases, straight or hooked and in some species swollen into hollow chambers. Leaves are bipinnate, divided into many small leaflets that fold in dry heat. Flowers form dense rounded heads or short spikes of yellow to cream, distinguishing the genus from related thorn trees with elongated flower spikes. Seed pods are flattened or coiled and constrict between the seeds.

Appearance

Size & Dimensions

Height3' - 98'

Width/Spread6' - 40'

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~4 weeks

Spring Summer

Flowering is concentrated in the warm season, from spring into summer, and in some species follows seasonal rains. Each flush of rounded heads lasts several weeks, releasing a sweet scent that draws bees and other insects. Pods ripen over the following months.

Detailed Descriptions

Flower Description

yellow to cream

Foliage Description

green to grey-green

Growing Conditions

Sun Requirements

SunFull Sun

Requires 6-12 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range6.0 - 8.5(Alkaline)

357912

Soil Types

sand loam rocky

Drainagewell drained

Water & Climate

Water Needs

Low

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Plants grow in full sun on free-draining sand, loam, or rocky ground, and tolerate low fertility. Established trees withstand extended drought through deep roots, while waterlogged soil causes root decline. Most species are frost-tender and are grown outdoors only in warm-temperate to tropical zones. Young plants grow quickly given warmth and occasional deep watering, then need little supplemental water once established. Saline and alkaline soils up to about pH 8.5 are tolerated across much of the genus.

Pruning

Lower branches are removed on young trees to raise the canopy where clearance is needed. Crossing or damaged wood is taken out in the dry season to limit gum bleeding. The spines make close work slow, and growth resumes readily after cutting.