Diosma haelkraalensis I.Williams
Common names: Hagelkraal bitter-buchu (Eng.); Hagelkraal bitterboegoe (Afr.)
This extremely hardy buchu thrives in both alkaline and acidic soils of the fynbos, and flowers for much of the year.
Small, closely leafy, decumbent, aromatic shrub, up to 400 mm high. The leaves are oppositely arranged and recurving. There are a few white flowers in each inflorescence. Flowers have 5 petals and 5 stamens. The style is not conspicuous at the time of pollination. The stigma is capitate. In the middle of the flower is a fleshy, green to yellowish green, cup-shaped, nectariferous disc, with wavy margins.
The fruits have distinctive long horns.
Flowering is from autumn until spring, (April to September).
According to the Red List of South African plants, the conservation status of this plant is Endangered (EN). It is a rare species, known from only 3 locations, which continue to decline due to competition from alien invasive plants. There is also a strong possibility that one location may be used as the site for a nuclear power plant.
Distribution and habitat
The Hagelkraal bitter-buchu is a range-restricted endemic species, found from Pearly Beach to Hagelkraal in the Western Cape. This species occupies crevices on limestone outcrops amongst Agulhas Limestone Fynbos, Agulhas Sand Fynbos and Overberg Dune Strandveld.
Derivation of name and historical aspects
The name Diosma, means ‘divine odour’ and is derived from the Greek dios, meaning ‘divine’, and osme, ‘odour’, referring to the scent of the leaves when crushed. Haelkraalensis means ‘from Hagelkraal’ and refers to the wild locality of this species.
The genus Diosma consists of 28 species, which are all small shrubs.
Diosma haelkraalensis forms part of a group of fynbos plants that grow on alkaline soils found on limestone outcrops along the coast, from Gansbaai to the Gouritz River. This specific group of plants is known as proteoid limestone fynbos, so named due to Protea species representing the majority of the species. It is restricted to the Bredasdorp geological formation Bredasdorp-Riversdale centre of endemism. This particular formation was integral in the evolution of various new fynbos species in this new habitat and soil conditions. Due to urbanization, agricultural expansion and alien invasive plants, limestone fynbos is now considered one of the most threatened vegetation types within the Cape Floristic Region.
Beetles and bees have been observed on plants during flowering and they could, therefore, both be potential pollinators.
No medicinal or cultural uses have been recorded, but this does not mean that this buchu was not used by the Khoisan people, who lived in this region in the past. Khoisan people used buchus to treat stomach complaints and mixed dried leaves with animal fat, to make a fragrant oil for rubbing on the body.
Research indicates that the Hagelkraal bitter-buchu contains the same sulphur-containing compound (8-mercapto-p-methan-3-one) that gives the characteristic odour to commercial buchus, such as Agathosma betulina and A. crenulata. This species, therefore, offers economic potential in the spheres of medicine and cosmetics.
Growing Diosma haelkraalensis
Sow the seed in autumn, using a medium that is light and has good drainage. A mixture consisting of equal parts of sand and compost or plain, coarse river sand can be used. Cover the seed with a thin layer of bark, sand or the medium and then water. Keep the seed tray in a covered area that provides enough good light and ventilation. Never allow the medium to dry out completely, or to be overwatered. The appearance of the first 4 true leaves, after 4–9 weeks, indicates the readiness of the seedlings for pricking out. Like all buchus, the fine roots must be handled with care.
The potted plants are now placed in a shady area for 3–4 weeks to harden them off, before placing in the sun. This will also be a good time to pinch out the growing tips of the seedlings, as this promotes a more bushy growth habit. Some nurseries also plant small buchu seedlings or plantlets grown from cuttings, in plugs after rooting. By using the plugs, the mortality rate is being decreased, plants grow quicker and plants get to be pruned between 2–3 times before being transplanted into larger bags. Regularly feed the young seedlings with some balanced nutrient products. Plants will be ready for transplanting into the garden after 8 to 9 months.
The taking of heel, tip or semi-hardwood cuttings is another way of propagation and will be the quickest way of achieving a flowering plant. Prepare cuttings of between 25–55 mm, remove about a third of the foliage and cut them below the node. Dip the cuttings in a rooting hormone and place in trays with a medium consisting of equal parts of bark and polystyrene. The cuttings are now placed in a mist-unit with heated benches. It takes 9–11 weeks for roots to develop. The rooted cuttings can then be moved to hardening-off for 2–3 weeks.
Pot the rooted cuttings in a well-drained soil mix and place in a shady area for 2–4 weeks to harden off. After this, they can be moved into full sun.
Diosma haelkraalensis will thrive in full sun, in well-drained and stony or rocky soil, where it is planted amongst other fynbos species. The ideal time for planting is between autumn and winter, which is the rainy season in the fynbos. This will enable plants to have a better chance of becoming established in the garden, before having to cope with the drought and extreme heat of summer.
Plant this buchu with: Acmadenia heterophylla and A. mundiana, Agathosma apiculata, A. collina, A. gonaquensis and A. serpyllacea, Coleonema album and C. pulchellum, Cotyledon orbiculata, Euchaetis meridionalis, Helichrysum dasyanthum, Restio dispar, Lampranthus aureus, Leucospermum patersonii, Lobelia valida, Pelargonium betulinum, Protea compacta and P. obtusifolia.
Planting at intervals of 20 to 30 cm, should provide enough space to encourage growth. This relatively dense planting is preferred by buchus, as it helps to retain soil moisture. Provide a good, thorough watering in winter. In summer, watering should just be moderate; however, do not allow plants to dry out completely. Regular mulching also aids in keeping the roots and soil cool in summer.
- Gould, M. 1992. The buchus: cultivation and propagation. National Botanical Institute, Cape Town.
- Heydenrych, B. 1994. Buchu oil from Hagelkraal’s diosma? Veld & Flora 80 (2). Botanical Society of South Africa, Cape Town.
- Heydenrych, B., Willis, C. & Burgers, C. 1994. Limestone fynbos. Veld & Flora 80 (3). Botanical Society of South Africa, Cape Town.
- Manning, J. & Goldblatt, P. 2012. Plants of the Greater Cape Floristic Region 1: the Core Cape Flora. Strelitzia 29. South African National Biodiversity Institute, Pretoria.
- Powrie, F. 1998. Grow South African Plants. A gardener's companion to indigenous plants. National Botanical Institute, Cape Town.
- Trinder-Smith, T.H. 2003. The Levyns Guide to the plant genera of the south western Cape. Bolus Herbarium, UCT, Red Roof Design CC, Cape Town
- Trinder-Smith, T., Raimondo, D. & Zikishe, V. 2012. Diosma haelkraalensis I.Williams. National Assessment: Red List of South African Plants version 2017.1. Accessed on 2017/07/19
Kirstenbosch National Botanical Garden
Plant Type: Shrub
SA Distribution: Western Cape
Soil type: Sandy, Loam
Flowering season: Spring, Autumn, Winter
PH: Acid, Alkaline, Neutral
Flower colour: Green, White
Aspect: Full Sun
Gardening skill: Easy