Streptocarpus cyaneus S.Moore
Common names: Cape primrose (Eng.)
Streptocarpus cyaneus is very attractive and is one of the few species of Streptocarpus that produces either white, pink or blue flowers depending on their distribution.
This plant is a perennial herb with a horizontal rhizome but no true stem. The leaves are arranged in a loose rosette and grow directly from the base of the plant. They are slightly hairy and measure around 400 mm in length.
The main characteristic feature of the flower is a marked yellow stripe in the centre at the base of the corolla, which also has reddish-violet streaks which extend to the lower lobes of the corolla. As mentioned, the colour of the flowers may be white, pink or blue depending on the distribution. There are between 2 and 12 flowers on each inflorescence, which grow on a flower stalk above the leaves which is about 200 mm long. The flowers are asymmetrical; the upper lobes are 8-18 mm long, the lower lobes 15-25 mm long. All the lobes are medium violet or rose pink and very occasionally white. The seeds are 0.5-0.7 mm long and are reticulate (with a network-like pattern). Flowering time is in summer, from October till February.
According to the website http://redlist.sanbi.org, checked on 9 November 2015, Streptocarpus cyaneus subsp. cyaneus, S. cyaneus subsp. nigridensis and S. cyaneus subsp. polackii are all classified as Least Concern (LC) and are not threatened, but Streptocarpus cyaneus subsp. longi-tommii is Vulnerable (VU). This subspecies has only six known localities in the Long Tom Pass to Kaapsehoop area, and they are all potentially threatened by invasive alien plants.
Distribution and habitat
Streptocarpus cyaneus can be found in the northern and southern parts of KwaZulu-Natal. There is also an isolated population in Kranskop, KZN. In Swaziland it can be found in Mbabane and Piggs Peak. There is also a large S. cyaneus population in the forests between Hlatikulu and Goedgegun in the Usutu River valley.
The natural habitat of this plant includes rain in summer, well-drained soils, an average amount of shade with dappled light and good ventilation. The plant does not tolerate too much heat and wet soils.
Derivation of name and historical aspects
The first Streptocarpus species, found in 1818 by James Bowie, was named Didymocarpus rexii, now known as Streptocarpus rexii. The name Streptocarpus is derived from the Greek streptos = twisted and karpos = fruit.
The genus Streptocarpus is a member of Gesneriaceae, a family with more than 100 genera and more than 2000 species. The family is characterized by flowers that are zygomorphic, i.e. they are symmetrical about only one plane. Most members of the gesneriad family are herbs but there are also some shrubs and small trees.
The Gesneriaceae family comprises mainly epiphytic plants,i.e. plants growing on other plants, such as trees, without deriving nourishment from them, and lithophytic plants, i.e. plants growing on rocky outcrops. They also grow in forests and along streams. The seeds of Streptocarpus species are very small and light and are distributed by the wind.
Streptocarpus species are beautiful plants, very rewarding for people who love lots of colour. They make excellent plants for the show bench and are an absolute winner when it comes to display shows or even just displays at your home. They are mainly used for indoor displays. Even within a year of growth they can produce magnificent flowers and put on a good display. Streptocarpus species and hybrids have been used in various display shows including the Chelsea flower shows.
Growing Streptocarpus cyaneus
Streptocarpus cyaneus requires bright, dappled sunlight and conditions must not be too hot. If the plant receives full sun the leaves and flowers will burn and shrivel. If there is insufficient light, the plants will end up producing very large leaves. They should be kept in a glass house or under shade netting. It would be preferable to put the streptocarpuses in a section that is north-facing. The area where they are kept must be well aerated/ventilated. The optimum growth temperature is about 20 degrees Celsius. If you are keeping them in your house then you must ensure that you keep them in a bright area.
Streptocarpus species grow very well on a medium containing peat-based compost. You can also use a coir-based compost but feeding must then start earlier. The established cuttings should be planted in a shallow pot. A 10-cm plastic pot would be preferable. A plant that is potted up in spring will probably be ready by mid-summer.
Frequency of watering of these plants depends on temperature, humidity and air movement. On days that are hot and dry much more water is needed than on cool damp days. The best way to know when to water your plants is by lifting up the pots and feeling the weight or by looking at the soil medium. This practice comes with experience. The most important factor is not to overwater your plants. You can water the plants from below or above. In summer frequent watering is required, whereas in winter less watering is required. Streptocarpuses are drought-tolerant plants.
Feeding Streptocarpus should commence in February or March, starting with an average feed and gradually increasing it to once a week, using the manufacturer's recommended strength. It is best to use a slow-release fertilizer and that is high in potash as this will encourage better flowering and development of better flowers.
When the flowering is finished, the dead flower stalks should be removed /cut off as low as possible. This will encourage better flowering the next time the plant flowers. You will find that the leaves often die back at the tips. This is normal. In some cases you will find that all the leaves die off and the plant becomes bare. This happens to allow for the development of the new leaves.
If you are planting Streptocarpus outdoors, make sure that the area is frost-free. Streptocarpus will die if exposed to frost. They need a sheltered area with no wind and some shade. The area must not be waterlogged.
Streptocarpus can be grown either from seed or cuttings.
The preferred method is leaf cuttings. Use secateurs, a sharp knife or blade to make the cutting. Make sure you sterilize the implement before making the cutting. Always use a healthy, dark green whole leaf from the centre of the plant. This is where vigorous growth is obtained. You can cut either side of the midrib to get cuttings. The leaf cutting should be about 10-15 cm long. Do not use old, unhealthy leaves as these will not root. The soil medium for rooting varies. You can use normal potting soil mix or a mix of peat-based potting compost with an equal amount of vermiculite. The mix that works well is: 40% perlite, 40% potting soil mix and 20% coarse river sand (coarse Umgeni sand). The cuttings should be placed 25 mm deep. They must then be put in a bright area and not in full sun. The cuttings can also be placed in a greenhouse or under shade netting. They normally take about a month to root. After two to three weeks you will see the young plants appearing from the base of the cuttings. Always ensure that the medium is kept moist but not wet. If you want to propagate more plants then you can cut each leaf transversally into several pieces. Each piece must be between 50-75 mm long. Make sure the centre pieces of the leaves are planted the correct way up. Once the young plants are between 30-50 mm tall they can be planted into bigger pots.
Making leaf cuttings requires a lot of skill and patience. The best way to get it right is to keep practising this method as this will build up your experience over time.
For seed sowing you can use either seedling mix or normal potting soil. Because the seeds are so tiny it is important to scatter them evenly, using your hands, on the top of the soil medium. Do not cover the seeds with any soil. Give them a gentle watering /spray and then put them into the greenhouse /shade netting area. The trays must be kept within a temperature range of about 20°C. The area must be bright but it must not be exposed to full sun. Always keep the soil moist but not very wet. The tiny seedlings will normally appear within two to three weeks. Once the seedlings are between 5-6 mm tall you can transplant them into a plastic pot /container. It is preferable to use a 100 mm pot to plant them in.
Streptocarpus species are prone to a number of pests and diseases. This can be prevented to some extent by using good growing techniques and preventing the plants from being stressed. It is important to enforce good hygiene methods. Always use sterile compost and sterilize any pots/seed trays that have been used before. It is very important to inspect your plants regularly. Try to do this on a daily basis. This will help you to see any problems developing early on, and then preventative measures can be taken. Try to ensure that the plants are kept/planted in a weed-free environment. Weeds tend to harbour pests and diseases. In order to prevent fungal diseases ensure that the area is well ventilated. Also avoid excessive sunlight and overwatering as this encourages fungal-disease build up. The commonest pest is worms. When spotted, try to spray them as soon as possible using a pesticide recommended for them. Other types of pests that attack Streptocarpus are aphids, which are small and can be black or yellow, bumble bees, leaf mealy bugs, which are powdery white, and snails. The fungal diseases include grey mould and powdery mildew.
- Burtt, B.L. & Hilliard, O.M. 1971. Streptocarpus, an African plant study. University of Natal Press, Pietermaritzburg.
- Dibley, R. 2003. Streptocarpus. Dibleys Nurseries, North Wales.
- Raimondo, D., Von Staden, L., Foden, W., Victor, J.E., Helme, N.A., Turner, R.C., Kamundi, D.A., Manyama, P.A. (eds) 2009. Red List of South African plants 2009. Strelitzia 25. South African National Biodiversity Institute. Pretoria.
- Zimmer, G.F. 1912. A popular dictionary of botanical names and terms. Broadway House, London.
KwaZulu-Natal National Botanical Gardens
Plant Type: Perennial
SA Distribution: KwaZulu-Natal
Soil type: Loam
Flowering season: Spring, Early Summer, Late Summer
Flower colour: Blue, White, Pink, Mauve/Lilac
Gardening skill: Challenging