Petalidium oblongifolium C.B.Clarke
Common names: blue petalidium, blue petal-bush (Eng.); bloubos, blou-tongklapper (Afr.)
A beautiful small shrub with silvery leaves and attractive blue flowers in summer; a hardy, water-wise plant for sun or semi-shade.
Petalidium oblongifolium is a small, much-branched, evergreen shrub, 400–600 mm tall. The leaves are simple, opposite, firm, broadly lanceolate, upward pointing, silver-grey and sometimes appear to have a metallic hue.
Large purple-blue flowers, which are similar to those of Barleria, grow from the leaf axils. The flowers are tubular and arise between 2 large purple bracts that enclose the calyx and turn brown with age.
It has a long flowering season, starting in spring and continuing into winter (October to July).
The wild population of Petalidium oblongifolium is stable, it is not facing any direct threats, and it is, therefore, assessed as Least Concern (LC) in the Red List of South African plants.
Distribution and habitat
Petalidium oblongifolium grows in bushveld in Mpumalanga and Limpopo Provinces.
Derivation of name and historical aspects
The genus name Petalidium is derived from the Greek petalon, which is a leaf or petal. The species name oblongifolium means with oblong leaves. There are more than 30 species in the genus. Petalidium oblongifolium is one of the 29 species which have been recorded in southern Africa.
It bears flowers almost all year round. The flowers produce copious nectar that attracts and feeds many pollinating insects.
In Limpopo Province it has been observed that cattle and goats, and game, browse Petalidium oblongifolium, especially in autumn and winter when grazing is scarce. Farmers notice that the animals that eat this plant thrive, but are not sure if this is because of any medicinal properties of the plant, or its nutritional qualities. A study by Mokwala (2007) isolated antibacterial compounds in Petalidium oblongifolium that were shown to be active against Ehlrichia ruminantium, which causes the heartwater illness in livestock. Petalidium oblongifolium is, therefore, of medicinal benefit to browsing animals.
Some petalidiums are cultivated as ornamentals, as they grow fast and flower profusely.
Growing Petalidium oblongifolium
Propagate by seeds sown in spring or early summer or by cuttings taken in summer.
Grow it in full sun or semi-shade, in well-drained soil. It is frost hardy and drought resistant, and will tolerate quite harsh conditions. Best suited to bushveld and grassland gardens. Plant it en masse as a groundcover, in groups in a mixed border or in a rockery. It is suitable for containers. Prune it back in late summer to early autumn to keep it low and bushy.
- Germishuizen, G. & Fabian, A. 1997. Wild flowers of northern South Africa. Fernwood Press, Vlaeberg, Cape Town.
- Jackson, W.P.U. 1990. Origins and meanings of names of South African plant genera. University of Cape Town.
- Joffe, P. 2003. Easy guide to indigenous shrubs. Briza Publications, Pretoria.
- Mokwala, P.W. 2007. Antibacterial activity of plants that are used in the treatment of heartwater in livestock and the isolatio of bioactive compounds from Petalidium oblongifolium and Ipomoea adenoides. PhD Thesis, University of Pretoria.
- Random Harvest, Petalidium oblongifolium. https://www.randomharvest.co.za/en-us/South-African-Indigenous-Plants/Show-Plant/PlantId/478/Plant/Petalidium-oblongifolium. Accessed 31 March 2020.
- Victor, J.E. 2005. Petalidium oblongifolium C.B.Clarke. National Assessment: Red List of South African plants version 2017.1. Accessed on 2020/03/31.
- Wikipedia Petalidium. 2020 https://en.wikipedia.org/wiki/Petalidium. Accessed 31 March 2020.
- Wild Flower Nursery, Petalidium oblongifolium. https://wildflowernursery.co.za/indigenous-plant-database/petalidium-oblongifolium/ Accessed 31 March 2020.
Free State National Botanical Garden
Acknowledgments: Andrew Hankey of the Walter Sisulu National Botanical Garden is thanked for providing images of the flower.
Plant Type: Shrub
SA Distribution: Limpopo, Mpumalanga
Soil type: Sandy, Loam
Flowering season: Spring, Early Summer, Late Summer, Autumn
Flower colour: Blue, Purple
Aspect: Full Sun, Morning Sun (Semi Shade), Afternoon Sun (Semi Shade)
Gardening skill: Easy