Walking down the Camphor Avenue at Kirstenbosch, one can not but stop to admire the clumps of Streptocarpus formosus flowering on the ground. Formosus meaning beautiful, is a perfect description of this species with its trumpets of soft mauve flowers. In nature they grow around Port St Johns in the Transkei and the sandstone gorges of Umtamvuna and Oribi, in Kwazulu-Natal. In these sub-tropical forests the summers are humid and wet, while the winters are warm and dry. Streptocarpus formusus is found along the gorges, growing in pockets of well-drained soil between the rocks.

Streptocarpus are fascinating for each leaf is an individual plant with its own roots and flowering stems. Streptocarpus formosus plants form thick clumps of long, strappy leaves arranged in a rosette. The dark green leaves are almost succulent with many little, white hairs. The veins of the leaves are very prominent, especially on the underside where the midrib and side branches form thick ridges. The tips of the leaves often die off as they get older and when stressed by drought or low temperature. Although the brown ends may look unattractive, this survival tactic does not harm the plants. The leaf simply forms an abscission layer and continue with new growth from the base.

Streptocarpus formosus flowers almost throughout summer, from late spring to autumn. One or two flowers are formed at the tips of the long flowering stems. Each leaf usually has a few flowering stems of different ages, growing from the base. The large trumpet-shaped flowers are white with soft mauve markings that run along the edge of the petals and into the distinctive, yellow-floored throat. Each delicate flower lasts a few days even when cut for the vase. The plants cross-pollinated easily with other species or in many instances are self-pollinated. Thousands of fine brown seeds are released within a month or two from long fruits. When dry, the fruits have an interesting way of unfolding like a spiral and hence the name Streptocarpus which means " twisted fruit" in Greek (streptos = twisted and carpus= fruit).

Growing Streptocarpus formosus

In most collections plants come and go, with a few surviving the good and the bad times. At Kirstenbosch Streptocarpus formosus has proven to be one of the most reliable and beautiful, flowering as pot plants in the glasshouse and planted out in the garden. In a mild climate like Kirstenbosch, the plants survive the winters outside as long as they do not get too wet. Watering streptocarpus should be done with care. Give a thorough watering only when the plants are dry. During the warm summers they are actively growing and need plenty of water, but during the cool winters very little water should be given. Streptocarpus should rather be under watered than over watered. Even when slightly wilted from drought, they will quickly recover with a good watering. Often plants look wilted when over-watered, so feel the soil before watering. Plant streptocarpus in a well-composted medium with good drainage. The soil mixture sold at nurseries for African violets usually works well. The plants are very sensitive to light, easily burned by sun and reluctant to flower in deep shade. Light shade with good ventilation is best for growing healthy plants with plenty of flowers. Streptocarpus respond well to feeding during summer when they are actively growing. Removing the dead leaves and flowers regularly keeps the plants attractive and healthy.

Propagation

Streptocarpus formosus can be propagated from a single leaf. Simply break of a young, healthy leaf at its base and place it in a well-drained medium like sand or compost. If many new plants are required, the leaf can be cut along the midrib or horizontally into segments. Wedge the cut edges into the rooting medium. Water thoroughly and place the cuttings in the shade. Within a month or two, new leaves will form along the edge placed in the rooting medium. The old leaves turn brown and dead as the young leaves start to grow. Once the new plants are well established, they can be potted into small pots and grown on. To get new plants identical to the parents, it is best to propagate from cuttings.

Streptocarpus formosus can also be propagated from seed sown during the warm spring and summer months. Carefully scatter the seeds on a moist, well-drained medium and place in a spot with good light but not direct sunlight. Water regularly with a fine spray not allowing the seedlings to dry out. Germination is usually within a month. Plant the seedlings into small pots only once they are quite big and strong. Transplant again into bigger pots when the roots have filled the small pots. Mature plants often loose their vigor after about 3-5 years and should be replaced by younger plants.

Streptocarpus and African violets belong to the same family, Gesneriaceae. More than 100 species of Streptocarpus are found widespread from central Africa to South Africa and Madagascar. Most of the species are found in southern Africa, but it is in Europe and America that streptocarpus is well known as a pot plant. In 1826 the collector James Bowie took the first plants of Streptocarpus rexii to Kew Botanical Gardens in England. As more species were introduced into cultivation different hybrid streptocarpus were produced. Today new hybrids are still introduced to the huge and growing pot plant market, with growers like Dibleys' Nursery in Wales specializing mainly in streptocarpus. Rex and Gareth Dibley have written a Wisley handbook full of interesting facts and tips on growing streptocarpus that can be consulted for more information.

Author: Liesl van der Walt
Kirstenbosch
January 2001