Oldenburgia paradoxa is an unusual cushion-shaped species of the daisy family that grows on rocks in the Cape Mountains and looks like an alpine plant. It forms tight, hard, woody mounds from which its flower-heads peek between the dark-green leaves.
Olenburgia paradoxa is a dwarf, cushion-forming shrublet, up to 0.3 m in height, with short, thick woody branches. The pllants form cushions up to 1 m in diameter on rocky outcrops. Leaves are narrowly-elliptic, alternately arranged to form rosettes at ends of short branches. They are 10 – 50 mm long, about 10 mm wide, shiny, dark green, simple, leathery. The undersides are densely white-woolly and the leaves are silky at base, with edges rolled under.
The plants produce a number of single, stalkless, tan-coloured capitula (flower heads) that nestle in the cushion of leaves. Each capitulum is about 25 mm in diameter with several rows of firm, woolly bracts and small white florets in each head. Plants flower from January to October with a peak in April.
This species is listed as LC (Least Concern).
Oldenburgia paradoxa grows in high altitude mountain fynbos in the south-western and southern Cape from Villiersdorp to Avontuur.
Derivation of the name and historical aspects
The genus Oldenburgia was named in honour of F.P. Oldenburg, who accompanied Thunberg and Masson on some of their travels in the Cape in the early 1770s. The genus consists of four species that are endemic to the Cape Province.
Oldenburgia paradoxa grows on rocks of Table Mountain Sandstone, rooting in crevices and forming large cushions at 600 – 1 300 m altitude. It is a compact cremnophyte or cliff dweller with a strong root probing crevices to fix it securely to cliffs and rocky outcrops. The root zone is therefore restricted, well drained and acidic. Observations indicate that it is killed by fire, but some escape by habitat or survive partial burning. This species forms a very hard cushion and is not grazed.
Seed is released when flowers mature and each disc floret forms a small parachute, with the seed at the base, that can be distributed by wind. It appears not to colonise sandy soils on open slopes, which suggest that seeds need to land in a rocky crevice to germinate and survive to adult stage.
Oldenburgia grandis is pollinated by Cape sunbirds and it is therefore possible that they also pollinate Oldenburgia paradoxa.
Uses and cultural aspects
Oldenburgia paradoxa is a novelty plant that will be of interest to specialist plant collectors or growers of alpine-like plants.
Growing Oldenburgia paradoxa
Oldenburgia paradoxa is grown from seed that has been treated with smoke or smoke extract.
The seeds are then sown into a well-drained, acidic, potting mixture and lightly covered. Place seed in trays, plugs or individual pots and keep in a well-ventilated, warm, sunny position where the seeds are protected from rain. Sowing directly into plugs or pots minimizes root disturbance and maximizes the number of surviving seedlings. Do not over water and allow the medium to dry out a little between watering. The seeds should germinate within two months.
It is good practice to protect the seeds from rotting by treating them with a pre-emergence fungicide for preventing damping off. These fungicides are available at your local nursery. The seedlings should be carefully potted at cotyledon stage before the first pair of true leaves develop, as this species does not react well to disturbance. Choose the smallest pots or grow-plugs available and well-drained, acidic soil to mimic the natural crevice habitat to which it is adapted. A mixture of equal parts of well-rotted pine bark or fine compost and coarse river sand is recommended. The small plants should be fed every week or second week with an organic liquid fertiliser. The seedlings are slow growing and should be kept in the smallest possible container and only re-potted when it becomes root-bound and difficult to water.
Oldenburgia paradoxa form such a tight cushion that selection of cuttings is not recommended. They might root, however, removal of cuttings will destroy the aesthetic form of the plant. Plants in pots at Kirstenbosch have been divided and survive as long as some root is retained on each section.
Oldenburgia paradoxa is a recommended as a pot plant as a special collectors specimen. It is slow growing and long lived.
References and further reading
- Bean, A. & Johns, A. 2005. Stellenbosch to Hermanus. South African wild flower guide 5. Botanical Society of South Africa, Cape Town.
- Bond, P. 1987. A revision of Oldenburgia (Asteraceae — Mutisieae) South African Journal of Botany 53: 493 – 500.
- Manning, J. 2007. Field guide to the Fynbos. Struik, Cape Town
- Manning, J. & Goldblatt, 2012. Plants of the Greater Cape Floristic Region 1: the Core Cape Flora. Strelitzia 29. South African National Biodiversity Institute, Pretoria.
- Vlok, J. & Schutte-Vlok, A.L. 2010. Plants of the Klein Karoo. Umdaus Press, Hatfield