1. Introduction & Taxonomy

Rhus angustifolia, commonly known as Willow Karee, is a small to medium-sized evergreen tree native to South Africa, where it grows along streams, in grasslands, and on rocky hillsides. Belonging to the Anacardiaceae family, it is one of the most versatile and widely planted indigenous trees in southern African gardens. Its graceful, willow-like foliage, drought tolerance, and attractive berry displays make it a popular choice for both urban and rural landscapes.

Searsia angustifolia, the willow karee or smalblaar, is a small, bushy, evergreen tree which is confined to the South Western Cape in South Africa.

Taxonomic Classification

Habitat and Distribution

Rhus angustifolia is native to various regions. The genus Rhus is characterised by its tree growth form.

Native Range & Distribution Map

The map below shows the native range and notable cultivation regions for Rhus angustifolia.

2. Morphology & Growth Form

Crown Form & Architecture

Rhus angustifolia typically develops a rounded, dome-shaped crown with a relatively short trunk relative to the canopy spread. This balanced form provides excellent shade and a pleasing natural silhouette.

Key Characteristics

• Height: 5-15m
• Growth Habit: Tree
• Growth Rate: Moderate under optimal conditions
• Leaf Type: Evergreen

Notable Adaptations

Willow Karee typically grows 4-8 m tall, occasionally reaching 10 m, with a rounded, spreading crown and somewhat drooping branches that give it a graceful, willow-like appearance. The bark is dark grey-brown and rough. Leaves are trifoliolate with narrow, linear-lanceolate leaflets 5-12 cm long, dark green and glossy, giving the tree its 'narrow-leaved' name. Small, yellowish-green flowers are borne in terminal panicles. The small, round, shiny drupes ripen from green to dark brown, persisting on the tree and attracting birds.

3. Reproduction & Propagation

The primary propagation methods for Rhus angustifolia: Seed, cuttings, or grafting.

Propagating Rhus angustifolia

Rhus angustifolia is dioecious, requiring both male and female plants for fruit production. Flowers are insect-pollinated. The small fruits are dispersed by birds. Seeds have a hard coat and benefit from scarification or soaking in warm water before sowing. Germination takes 4-8 weeks. Truncheon cuttings (large hardwood stakes) planted directly into the ground are a traditional and effective propagation method in South Africa.

Rhus angustifolia can be propagated from seed. Collect ripe fruit or seed pods and extract seeds. Many tree seeds have physical or physiological dormancy requiring scarification (nicking or soaking in hot water) or cold stratification before germination. Sow in a well-draining seed mix, keep moist, and provide warmth (20–25°C) and light.

Vegetative Propagation

• Cuttings: Take semi-hardwood cuttings in summer or hardwood cuttings in winter. Treat cut ends with rooting hormone and place in a well-draining medium (perlite/peat mix) under high humidity. Many tree species root readily from cuttings.
• Grafting: Grafting is widely used for fruit trees, ornamental cultivars, and species difficult to root from cuttings. Common techniques include whip-and-tongue, cleft, and bud grafting onto compatible rootstock.
• Air Layering: Useful for species difficult to root from cuttings. Wound a branch, apply rooting hormone, wrap with moist sphagnum and plastic, and wait for roots to develop (usually 2–6 months).

4. Cultivation & Planting

An adaptable species that grows in a range of soils from sandy to clay, including rocky and alkaline substrates. Full sun is preferred for best form and fruit production. Once established, it is very drought-tolerant. Regular watering during the first year ensures good establishment. Apply compost mulch annually. Little fertilizer is needed.

Soil Requirements

Rhus angustifolia grows best in deep, fertile, well-drained soil with a loamy texture. Most trees are adaptable to a range of soil pH values (5.5–7.5). Amend heavy clay soils with organic matter and grit to improve drainage and aeration.

Watering

Water regularly during establishment (first 2–3 years after planting). Once established, most trees develop deep root systems that access subsoil moisture. Supplemental irrigation during prolonged drought improves growth and reduces stress.

Light Requirements

Full sun to partial shade, depending on species. Most trees produce their best form, flowering, and fruiting in full sun. Some understorey species tolerate or prefer partial shade.

Temperature & Hardiness

• Optimal Growth: 15–30°C (59–86°F)
• Minimum Tolerance: -12°C (10°F)
• USDA Hardiness: Zones 8-11

Planting Guidelines

• Timing: Plant bare-root trees in late autumn to early spring during dormancy. Container-grown trees can be planted year-round but establish best when planted in autumn.
• Spacing: Allow adequate space for the mature canopy spread. Crowding leads to poor form, increased disease pressure, and competition for light and water.
• Depth: Plant at the same depth as in the nursery container. Do not bury the root flare — this is a common planting error that leads to slow decline.
• Staking: Stake only if necessary (exposed windy sites), and remove stakes after 1–2 years to encourage trunk strengthening.

Seasonal Care Calendar

Follow this season-by-season guide for optimal care timing throughout the year.

5. Diseases & Pests

Rhus angustifolia, like most trees, is generally resilient when growing in appropriate conditions. Most disease problems arise from environmental stress, poor planting, or mechanical damage.

Major Diseases

Root Rot (Phytophthora, Armillaria)

Root rot is the most devastating tree disease complex. Phytophthora thrives in waterlogged soils and attacks fine roots, while Armillaria (honey fungus) produces distinctive mushrooms at the base of infected trees. Prevention: ensure good drainage, avoid overwatering, and do not pile soil or mulch against the trunk.

Canker Diseases

Canker-forming fungi (Nectria, Cytospora, Botryosphaeria) invade through wounds, pruning cuts, or stressed tissue. Sunken, discoloured bark areas expand and can girdle branches or trunks. Prune out infected wood well below the canker margin. Prevent by avoiding bark injuries and maintaining tree vigour.

Leaf Spot / Anthracnose

Fungal leaf spots and anthracnose cause browning, spotting, and premature leaf drop. Usually more cosmetic than life-threatening. Improve air circulation, rake and destroy fallen leaves, and apply fungicides in severe cases.

Common Pests

• Borers — Wood-boring beetles and clearwing moths attack stressed trees. Maintain vigour through proper watering, mulching, and avoiding bark damage.
• Defoliators — Caterpillars, sawfly larvae, and leaf beetles can severely defoliate trees. Healthy trees usually recover from a single defoliation event. Apply Bt (Bacillus thuringiensis) for caterpillar control.
• Scale Insects & Aphids — Sap-sucking insects that weaken trees and produce honeydew, leading to sooty mould. Treat with horticultural oil or systemic insecticide.
• Spider Mites — Cause stippled, bronzed foliage in dry conditions. Increase humidity and apply miticide.

Additional Disease Notes

Generally pest- and disease-resistant. Psyllids may cause leaf curling on new growth. Aphids and scale insects occasionally appear but rarely require treatment. The species is resistant to most common garden diseases.

6. Pruning & Maintenance

Prune in late winter to shape and remove any dead or crossing branches. Willow Karee responds well to pruning and can be trained as a single-stemmed tree or multi-stemmed shrub. Regular light pruning keeps the crown tidy.

Pruning Principles

• Formative Pruning: Establish a strong central leader and well-spaced scaffold branches in the first 5–10 years. Remove co-dominant stems, crossing branches, and low branches that will need removal later.
• Maintenance Pruning: Remove dead, diseased, damaged, and crossing branches. Never remove more than 25% of the live crown in a single year.
• Timing: Prune deciduous trees during dormancy (winter) for major structural work. Summer pruning can be used for light corrective work and to slow vigorous growth.

Mulching

Apply a 5–10 cm layer of organic mulch (wood chips, bark, leaf mould) around the base of the tree, extending to the drip line if possible. Keep mulch 10–15 cm away from the trunk to prevent collar rot. Mulch conserves moisture, moderates soil temperature, suppresses weeds, and improves soil biology as it decomposes.

Fertilisation

Young trees benefit from a balanced slow-release fertiliser (NPK 10-10-10 or similar) applied in early spring. Established trees in good soil rarely need fertilisation. Avoid high-nitrogen fertilisers that promote soft, disease-susceptible growth.

7. Landscape & Agroforestry

An excellent choice for water-wise gardens, parking lot islands, street plantings, and small gardens. Its graceful form, evergreen foliage, and bird-attracting berries provide year-round interest. Tolerates urban pollution and compacted soils. Good for screening and as a shade tree for small areas.

Landscape Applications

• Specimen Tree: Plant as a focal point in lawns, parks, or large gardens where its form can be fully appreciated
• Shade Tree: Provides cooling summer shade for buildings, patios, and outdoor living areas. A single large shade tree can reduce cooling costs by 20–40%.
• Street / Avenue Tree: Suitable for urban planting in streets, plazas, and parks where space allows for mature canopy development.
• Wildlife Habitat: Provides nesting sites for birds, food sources (seeds, fruit, nectar), and shelter for diverse wildlife

Companion Planting

Create effective plant communities by combining with:

• Understorey Trees — Smaller trees and large shrubs that thrive beneath the canopy
• Ground Covers — Shade-tolerant perennials, ferns, and bulbs for the forest floor layer
• Climbers — Mature trees can support non-damaging climbers like clematis or jasmine
• Bulbs — Spring-flowering bulbs beneath deciduous trees take advantage of light before leaf emergence

8. Climate Adaptation & Hardiness

Hardy to USDA zones 8-11. Tolerates moderate frost to about -5 to -7 degrees Celsius once established. Young plants should be protected from severe frost during their first few winters. Well-suited to the varied climates of South Africa.

Hardiness Thresholds

• USDA Zones: 8-11
• Minimum Survival Temperature: -12°C (10°F)

Cold Protection Strategies

• Site Selection: Plant in sheltered positions with good air drainage (avoid frost pockets). South- or west-facing walls provide radiated warmth and wind protection.
• Mulching: A deep mulch layer (10–15 cm) over the root zone insulates roots from freezing temperatures and reduces soil temperature fluctuations.
• Wrapping: Protect the trunk and scaffold branches of borderline-hardy trees with horticultural fleece or hessian during severe cold events. This is especially important for young trees during their first few winters.
• Container Growing: Trees in containers can be moved to frost-free locations for winter. Use large, insulated containers to protect roots from freezing.

Heat & Drought Adaptation

Many trees develop deep taproots and extensive lateral root systems that access water well beyond the canopy drip line. Drought adaptations include deciduousness (shedding leaves to conserve water), thick bark, small or waxy leaves, and the ability to close stomata rapidly during water stress.

9. Ethnobotany & Cultural Significance

In traditional South African medicine, bark decoctions of Rhus angustifolia are used to treat diarrhea and dysentery. The tannin-rich bark has also been used in leather tanning. The fruits were historically eaten by indigenous peoples and are an important food source for birds. The tree's drought tolerance and ease of cultivation have made it a staple of water-wise indigenous gardening in South Africa.

Frequently Asked Questions