Knowltonia vesicatoria is one of the few and best fynbos plants for the shady garden. Tough and water-wise, a mature clump of this plant with its attractive foliage, makes a striking feature under trees.
Knowltonia vesicatoria is a perennial herb with a tuft of leathery, dark green leaves up to 1.2 m tall. The leaves are divided into three leaflets and attached with leaf stalks to a short horizontal rootstock that is firmly anchored by fleshy roots.
The pretty, small white or yellowish green flowers are borne in clusters just above the foliage, mainly in spring (Aug.-Oct.).
The flowers are followed by attractive fleshy fruits that turn black as they ripen.
The blisterleaf grows slowly but has a long lifespan, with young plants producing only a few new leaves a year.
Knowltonia vesicatoria is not threatened.
Distribution and habitat
Knowltonia vesicatoria occurs widespread within the fynbos of the Cape, from the Bokkeveld Mountains near Nieuwoudtville, south to the Cape Peninsula and eastwards to Knysna, Port Elizabeth and Grahamstown. It grows in the shade of bushes, wooded patches, forests, kloofs and river valleys. Variable and adaptable, K. vesicatoria is found from sea level to 900 m, in sandy coastal dunes and soil rich in humus. Knowltonia vesicatoria subsp. grossa, a tall and robust plant from the southern Cape, is most probably the best form for gardens with its large leaves, random flowering throughout the year and adaptation to the local year-round rain. Frost is not common in its natural habitat, but it should be able to withstand light frost with its underground rootstock. Knowltonia vesicatoria is best suited to areas with a Mediterranean climate.
Derivation of name and historical aspects
Part of the Ranunculaceae family, Knowltonia is closely related to the genus Anemone, which includes popular garden perennials with colourful, cup-shaped flowers. The first Knowltonia known to European botanists was K. vesicatoria which l'Obel described as ' Ranunculus perelegans D. Franqueville, foliis aculeatis' in 1655. Salisbury described the new genus Knowltonia in 1796, naming it after Thomas Knowlton (1691-1781) an eminent English gardener at the botanical garden at Eltham.
Knowltonia is a southern African genus with five species from the Western Cape, two from the coast of KwaZulu-Natal and a single species widely distributed northwards from Gauteng to Tanzania. Knowltonia vesicatoria is distinguished from the other species by being glabrate (hairless) and by the characteristic teeth of the leaf margin. The three subspecies that are recognized are. subsp. vesicatoria, subsp. humilis and subsp. grossa. The species name vesicatoria is from the Latin vesicare that means to raise blisters, this refers to the strong allergic reaction caused by the leaves and roots. The Afrikaans common name brandblaar also refers to the allergic skin reaction.
Knowltonia has adapted to survive fire which is part of the fynbos rejuvination cycle, by resprouting from its underground rootstock.
Uses and cultural aspects
Many species of the Ranunculaceae family contain a toxic irritant oil which has prompted people to experiment with the medicinal uses of the plants. The early settlers at the Cape recognized Knowltonia as similar to European herbs such as Helleborus and it quickly became a popular herb with numerous uses. One was to use the leaves as a plaster over aching backs and joints. The burning sensation often causing blisters, was considered beneficial for treating arthritis and rheumatism. Colds and flu were treated with a tea made from the roots mixed with Pelargonium roots. Toothache was alleviated by placing a piece of root into the cavity of a decaying tooth.
Knowltonia vesicatoria is a popular plant for indigenous gardens, but plants are seldom available in the horticultural trade most probably because it grows so slowly.
Growing Knowltonia vesicatoria
The ripe seeds germinate easily, but the seedlings grow slowly and need patience. Sow the seeds in autumn (March) or as they start to drop from the old flower heads, in a seedtray filled with a well-drained potting mix. Cover the seeds with a thin layer of finely milled bark or sand. Place the seedtray in the shade and water regularly. Grow the young plants on in pots until the rootstock is strong before planting out into the garden; this can take a year or two.
Plant them in the shade and take care to select a special spot where they can establish themselves as a feature over time without strong competition from surrounding groundcovers. Plant it with other shade-loving groundcovers such as Asparagus, Plectranthus, crassulas, gasterias, Streptocarpus ; bulbs such a Drimiopsis maculata, Haemanthus albiflos, Scadoxus membranaceus or the small shrub Myrsine africana. The plants respond well to regular watering and a thick application of a compost mulch. Established plants with a strong underground rootstock will be able to survive dry periods.
K. capensis can also be grown in shady spots in the garden.
References and further reading
- Leistner, O.A. (ed.). 2000. Seeds plants of southern Africa : families and genera. Strelitzia 10. National Botanical Institute, Pretoria.
- Pooley, E. 1998. A field guide to wild flowers of KwaZulu-Natal and the Eastern Region. Natal Flora Publications Trust, Durban.
- Rasmussen, H. 1979. The genus Knowltonia (Ranunculaceae). Opera Botanica 53. Stockholm.
- Roberts, M. 1992. Indigenous healing plants. Southern Book Publishers, Pretoria.
- Smith, C.A. 1966. Common names of South African plants. Memoirs of the Botanical Survey of South Africa No. 35.
- Van Wyk, B.-E. & Gericke, N. 2000. People's plants: a guide to useful plants of southern Africa. Briza Publications, Pretoria.
- Van Wyk, B.-E., Van Oudtshoorn, B. & Gericke, N. 1979. Medicinal plants of South Africa. Briza Publications, Pretoria.
Liesl van der Walt