Nivenia corymbosa (Ker Gawl.) Baker
Common names: blue stars (Eng.); blousterretjie (Afr.)
This attractive shrublet, with striking blue flowers in late summer at the Cape, is an unusual member of the iris family.
Nivenia corymbosa is a shrublet which grows to a height of 0.5 to 2 m. The stems are erect to inclined, several growing from the base of the plant. The younger stems are 5-6 mm in diameter with the older stems reaching to 30 mm in diameter at the base. The narrow, lanceolate leaves are sword-shaped and are 100-200 x 8 mm. The inflorescence or corymb is large and has about 120 flowers borne on a terminal cluster. The flowers are usually pale to deep blue and appear from late January to March.
Nivenia cormybosa belongs to a group of plants known as the woody irises, which also include two other genera, Klattia and Witsenia. The 13 species in these genera are all evergreen shrubs which characteristically have the woody stems and woody underground caudex (swollen woody underground organ from which stems arise). Nivenia is the largest of the woody genera with nine species. Nivenia stokoei is another attractive species in cultivation.
Distribution and habitat
Nivenia corymbosa occurs in a small stretch of the western Cape mountains. It is more specifically found in the south of Bain's Kloof to the Tulbagh Waterfall, some 30 km to the north. The species prefer areas where moisture is available throughout the hot, dry summer. The plant grows close to water along seeps and streams, in crevices in cliffs and in rocky outcrops.
Derivation of name and historical aspects
Herbarium specimens indicate that an Scottish botanist and traveller, Francis Mason who collected specimens for Kew gardens, discovered the species. The species is, however, named after James Niven, an avid gardener and collector of plants, who was sent to the Cape in 1798 by George Hibbert, a wealthy Englishman. Niven collected seeds which were sent back and grown at Hibbert's Clapham estate in London. Ker Gawler placed the species in the genus Witsenia in 1805 and only in 1808 were they described as Nivenia. The species name corymbosa refers to the corymbs, which are flat-topped flowerheads.
The flowers are pollinated by a number of bees but the most important bee appears to be the large long-tongued Amegilla fallax (Anthophoridae). The roots of the plant are always wedged in between rocks: this is a possible adaptation to surviving in the wild. This prevents fires from totally destroying the caudex, which is resistant to fires. If the plants are growing in a fairly open area the possibility of a periodic fire will destroy plants, as the intensity of the fire can destroy the woody caudex.
Growing Nivenia corymbosa
Nivenia corymbosa can be propagated by seed and cuttings. Heel cuttings can be taken in autumn or spring, using actively growing side shoots or short new shoots taken off the caudex. A rooting hormone for hardwood or semi-hardwood cuttings should be applied to the cut surface of the stem. A good rooting medium is equal parts of 6 mm milled pine bark and polystyrene balls for aeration. Heated benches with mist are also recommended, although cuttings may also be rooted in coarse river sand in cold frames. They are very slow to root and the cutting often produces a callus and no roots. The cutting should be taken out of the rooting medium and retreated with a hormone after slightly damaging the callus. Place the cutting into fresh rooting medium. Roots are always very fine and brittle so care must be taken when handling and potting the plants.
Seed should be sown in autumn and treated with smoke for best results. Sow in a well-drained, acidic soil medium consistent with that used for other fynbos plants. The seedlings remain small for a long time so it is preferable to transplant into small individual pots and allow them to establish themselves before planting into a bigger container.
The plants growing in the container can be fed with seaweed-based, organic fertilizer such as Kelpak on a monthly base. If you have a particular area in your garden that is relatively moist, then this plant will be ideal, as it prefers growing in moist conditions. The species will require water in winter if it is grown in a summer rainfall region.
- Goldblatt, P. & Manning, J. 2000. Cape plants. A conspectus of the Cape flora of South Africa. Strelitzia 9. National Botanical Institute, Cape Town and Missouri Botanical Garden.
- Goldblatt, P. 1993. The woody Iridaceae. Timber Press, Portland, Oregon. The Plants Data Base: http://plantsdatabase.com/botanary/go/236/Author Trevor Adams & Anthony Hitchcock National Botanical Institute April 2004
Trevor Adams & Anthony Hitchcock
National Botanical Institute
Plant Type: Shrub
SA Distribution: Western Cape
Soil type: Sandy
Flowering season: Late Summer
Flower colour: Blue
Aspect: Full Sun
Gardening skill: Average, Challenging