Agathosma apiculata

G.Mey.
Family : Rutaceae (citrus and buchu family)
Common names : buchu ( Eng.); knoffelboegoe (Afr.)

Image of A. apiculata bloom

The leaves of Agathosma apiculata are aromatic and a distinctive garlic scent is released when the leaves are crushed, due to the volatile oils in the glands on the leaves and fruit, a recognisable fragrance unique to the Rutaceae (buchu) family.

Description
Agathosma apiculata is a densely leafy shrub, from 0.3-1.5 m high. It forms a single stem at the base and grows into a bushy and upright shrub. The branchlets are glabrous (hairless) or pubescent (covered with fine hairs). Younger stems are light brown and turn darker as they mature. The leaves lie perpendicular (horizontal) to the stem, are dark green, small, 2.5-8.0 mm long, alternately arranged and the apex forms a sharp point. White flowers at the tips of the stems cover the bush from April to January; 1-10 flowers with long stigmas are borne in terminal clusters. The petals are 3.5-4.0 mm long and hairless. The fruit is a capsule with 3 chambers, and each carpel contains one black shiny seed. The seed ripens in November to December.

Conservation status
Agathosma apiculata is not protected by any South African legislation.

Image of A. apiculata bush

Distribution and habitat
Agathosma apiculata occurs naturally on coastal dunes and grows in clays, on granite as well as limestone soils from Riversdale to Bredasdorp. This species has been collected at an altitude of 300 m.

Derivation of name and historical aspects
The genus name Agathosma is derived from the Greek agathos, meaning pleasant and osme, meaning smell or scent. The oil glands on the leaves and fruit release a sweet to strong fragrance when crushed. Agathosma apiculata belongs to the Rutaceae, commonly known as the citrus family. The genus consists of 150 species, and mainly occurs in the Western Cape. Barosma is the old name for Agathosma.

Image of bee visiting A. apiculata bloom

Ecology
Insects, bees and butterflies are attracted to the flowering bush for its nectar and are responsible for pollination.

The capsule splits through drying and the seeds are forcibly discharged. This is known as ballistic dispersal. Ants collect the seed, dispersed away from the mother plant.

Uses and cultural aspects
Agathosma apiculata is an attractive evergreen shrub suitable for coastal gardens as well as for fynbos or water-wise gardens.

Agathosma glabrata, A. gonaquensis, A. mucronulata and A. laceolata (honey buchu) are best used as a filler or accent plant in a mixed fynbos garden or as a potplant. Agathosma betulina (round leaf buchu) and A. crenulata (long leaf buchu) are commercially grown for their oil content. The oils in the leaves are extracted and used in the manufacturing of cosmetics, medicines, soaps and food colourants.

Image of A. apiculata bush

Growing Agathosma apiculata

Agathosma apiculata is a medium to large shrub and best used as a filler plant in a mixed fynbos garden. With its bushy growth and dark green leaves, it provides a texture contrast in a planting. It requires full sun, well-drained soil and can be planted in soil that is alkaline to acid. Before planting, prepare the garden bed by digging over the soil, adding compost and a slow-release fertilizer.

Plant during autumn, winter and spring with a combination of Pelargonium, proteas, aloes, restios, watsonias, Leucadendron and other interesting companion plants. Water the garden area before planting. Plant out in groups of three or five, 20-30 cm apart, with enough space to encourage growth. Buchus respond to a fairly dense planting which helps to retain soil moisture. The rainy season allows buchus to establish themselves in the garden and to cope with drought and less water during summer. Once established, they will withstand a fair amount of frost. Plants can be maintained in the garden for several years and are pruned once the bush becomes untidy.

Plants require good watering in winter and moderate watering in summer. Do not allow plants to dry out and avoid cultivating the soil around the roots of these fynbos plants. They are slow-growing plants and should not be planted too close to faster growing plants. A layer of mulch is added after planting and annually to keep soil and roots cool in summer-the mulch retains soil moisture and reduces germination of weed seed.

Agathosma apiculata can be propagated by sowing seed and by taking cuttings.

Collect seeds from the current year's capsules. Harvest the seeds after the first capsule has opened and place them in a closed paper bag or closed container (not plastic). Store it in a warm and dry place. You can hear the seed being expelled from the ripening capsule.

The optimum time for sowing is during autumn. Clean seeds and sow on a prepared medium of sand and compost in equal parts in a seed tray. Cover seeds with a thin layer of bark and water. Place seed trays in a covered area with good light and ventilation. Keep seed trays damp and germination will take place within one to two months. Prick out seedlings when four true leaves have developed. Take care not to damage the fine roots. Harden off the seedlings in shade for 3 to 4 weeks before placing them in the sun. Pinch out the growing tips of seedlings to encourage bushy growth. Feed buchus regularly with a balanced nutrient. The yellowing of leaves can be treated with an application of iron chelate. After 8 to 9 months the plants can be planted out in the garden.

Vegetative propagation (cuttings) is done from August to early October when suitable material is produced after flowering. Cuttings have the advantage of producing a larger flowering plant more rapidly than seedlings. Take heel- and semi-hardwood cuttings, 50-70 mm long, from the current year's growth. Prepare cuttings by making a clean cut below the node and remove a third of the foliage. Dip the base of the cuttings in a rooting hormone. Firmly place the cuttings in a medium of 50 % bark and 50 % polystyrene. Ideally, these cuttings should now be placed in an well-aerated propagation unit with a bottom heat of 24°C. Rooting should occur in 9-11 weeks. Carefully pot the rooted cuttings, using a well-drained, humus-rich, fynbos potting medium (2 parts leaf mould, 1 part coarse sand). Keep plants under shade for three weeks to harden off before being placed in the sun. Plants will be ready for planting in 7-8 months. Pinch back young buchu plants to encourage bushy growth. Once established, do not cultivate the soil around the root area.

Feed regularly with a well-balanced nutrient. Phytophthora cinnamonni a soil and water-borne fungus, attacks the roots of most fynbos species. High soil temperatures promote the growth of this fungus, attacking the plant's root system. It prevents the uptake of water, causing plants to die. Remove infected plants and use soil mulch to reduce the soil temperature. Disturb the soil as little as possible. Treat plants with a fungicide prior to planting out. This is a precautionary measure to control the fungus and to protect adjacent plants.

References and further reading

  • Brown, N. & Duncan, G. 2006. Grow fynbos plants. Kirstenbosch Gardening Series, Cape Town.
  • Gold, M. 1992. The buchus: cultivation and propagation. National Botanical Institute, Kirstenbosch.
  • Goldblatt, P. & Mannning, J. 2000. Cape plants. A conspectus of the Cape flora of South Africa. Strelitzia 9. National Botanical Institute, Pretoria & Missouri Botanical Garden, St Louis.

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Kirstenbosch National Botanical Garden
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