Plectranthus oertendahlii is a lovely shade-loving groundcover and very striking potplant with silver variegated leaves that are beautiful throughout the year.
Plectranthus oertendahlii has slightly succulent leaves and stems that root as they spread along the forest floor. It forms small, low clumps of about 200 mm high. The upper surface of the round, broadly serrated leaves is distinctly marked with silver veins whereas the underside is an attractive deep red. The plants feel slightly rough because of the short hairs on the leaves and stems.
Typical of the wild sage family, Lamiaceae, the stems are square-shaped. It flowers from late summer to winter (February to June) with a peak in autumn (April-May). The small whitish flowers often tinged with pink or mauve are held proudly above the leaves in upright spikes. The seeds are small brown nutlets held in the calyx that enlarges and remains after the white flower tubes have dropped. This fast-growing perennial germinates and flowers within one growing season but loses its vigour as it gets older.
This little plant is rare and difficult to find even in its natural habitat along the wooded river valleys on the coast of southern KwaZulu-Natal and Pondoland. It is not regarded as threatened, as a large part of its natural habitat is protected within the Oribi Gorge and Umtamvuna Nature Reserves.
Distribution and habitat
Plectranthus oertendahlii is endemic to a small area from the Oribi Gorge northwards to Uvongo. On the slopes of the forested valleys it grows with other succulents and other Plectranthus species such as P. fruticosus, P. ecklonii, P. saccatus subsp. saccatus, P. ernstii and P. oribiensis. The soil of the forest understorey is humus-rich, well drained and slightly acid. The rainfall along the moist subtropical coast is high (800-1 250 mm per year) and mainly in summer. Frost is absent.
Derivation of name and historical aspects
Plectranthus oertendahlii was grown in Europe long before its wild origin was known. By 1924, plants were described in Sweden and named after Ivan Anders Oertendahl, the head gardener of Uppsala University Botanical Garden. When, where and by whom these plants were collected and how they got to Sweden, nobody knows. Their natural habitat only became known after Lillian Britten, a botanist from Grahamstown, collected plants for a herbarium specimen in the Oribi Gorge in 1936. Ernst van Jaarsveld from Kirstenbosch made a special effort in 1977 to collect this rare plant and through his enthusiasm for this group, many Plectranthus species have been introduced into gardens. World-wide, there are about 350 species of Plectranthus that are widely distributed in Africa, India, Australia and Japan. In South Africa there are 53 species with many variations from tall shade-loving shrubs to vigorous groundcovers that grow in the sun. Plectranthus, also known as spurflowers (from the Greek plectron, meaning spur, and anthos, meaning flower), belongs to the large mint and sage family, Lamiaceae, known for its many medicinal and popular garden plants.
Growing on the forest floor, Plectranthus oertendahlii has adapted to survive the low light penetrating the tall tree canopy and strong root competition for moisture and nutrients.
The wine-red colour on the undersides of the leaves is due to the presence of the chemical anthocyanin which traps and stops light from going through. In its semi-succulent leaves and stems it stores the moisture collected by the fine network of shallow roots that run in the upper leaf litter layer where the deep-rooting trees have not penetrated. The stems that root where the plant touches the ground helps it to cover more ground in search of moisture and survive vegetatively if damaged by trampling animals or falling branches.
It flowers in autumn (April-May) when the plants are at their peak after the warm, growing and rainy season. The short-tubed flowers attract insects such as the honey bee ( Apis mellifera ), butterflies, bumblebees and bombyliid flies. To prevent self pollination, the pollen in the anthers ripen before the female part, the style which is part of the ovary. The plants produce plenty of seeds that ripen over the dry winter months and is are shaken out and dispersed locally, ready for germination with the summer rains.
Uses and cultural aspects
Plectranthus oertendahlii is a popular house plant in America, Europe and especially Scandinavia. A number of different cultivars such as Silver stars, Royal beauty and Lime light are available that have been selected for their attractive foliage and long flowering season.
Growing Plectranthus oertendahlii
Plectranthus oertendahlii is easy to grow, but needs to be renewed regularly to keep it vigorous. Grow the plants in the shade with regular water in summer if dry, but be careful not to over-water. If the plants receive too much light, the leaves turn yellow and the silver markings are not as prominent. Plant them in well-composted, loamy soil that is well drained. Choose a spot in the garden without competition from other stronger growing groundcovers and shrubs. Combine them with interesting shade lovers such as Clivia gardenii, Veltheimia bracteata, Streptocarpus formosus and Encephalartos villosus.
As mentioned, it is also lovely in a hanging basket and pots inside or outside the house. Prune the plants back after flowering to encourage new strong growth in spring.
Propagate new plants from seed or cuttings. Cuttings are easy to root and can be made throughout the year by tip cuttings placed into sand that is kept moist. At Kirstenbosch, we usually make the Plectranthus cuttings in early summer (November) to produce lovely full plants ready for display when they flower in autumn. Sow seeds in spring or early summer (October-November) in a well-drained medium. Germination is usually within three weeks.
The plants respond well to organic fertilizers during the summer growing season.
Most Plectranthus species are is affected by microscopic eelworm or nematodes which attack the roots and prevent the uptake of water and nutrients. Diseased roots will be swollen and knobbly. Make new clean plants from cuttings and replace the soil of pots and hanging baskets.
References and further reading
- Pooley, E. 1998. A field guide to wild flowers of KwaZulu-Natal and the Eastern Region. Natal Flora Publications Trust, Durban.
- Scott-Shaw, R. 1999. Rare and threatened plants of KwaZulu-Natal and neighbouring regions: a plant Red Data book. Kwazulu-Natal Nature Conservation Service, Pietermaritzburg.
- Van Jaarsveld, E. 2005. The southern African Plectranthus and the art of turning shade into glade. Fernwood Press, Cape Town.
Liesl van der Walt
To find out if SANBI has seed of this or other SA species, please email our seedroom