Senecio exuberans R.A.Dyer
Common names: none recorded
When Senecio exuberans was described in 1943 it was said to be 'one of the most characteristic features' of the grasslands around Pietermaritzburg (Dyer 1943). However, since then, most of these grasslands have disappeared under agricultural fields, urban and industrial development, and Senecio exuberans has become an example of how even common plants can become threatened with extinction if their habitat is not protected.
Senecio exuberans is a perennial herb. It has a thickened woody rootstock, but the above-ground parts are herbaceous. It grows up to 1.5 m tall when in flower, and stands out well above the surrounding grassland. The leaves are long and narrowly oblong, with long, slender petioles. The upper leaf surface is smooth and shiny green, whereas the bottom is duller with raised veins. The thickened leaf margins are wavy with rounded serrations (scalloped, or crenate). The plant has two types of leaves: the radical leaves are clustered around the bottom of the stem, and grow directly from the rootstock, while the cauline leaves are found along the stems. The radical and cauline leaves are similar in shape, except that the cauline leaves can be smaller and covered in thin, woolly hairs.
It flowers during December and January. It has yellow inflorescences that are borne on the tips of the tall, branched flowering stems. The inflorescence, typical of the daisy family (Trinder-Smith 2003), consists of many tiny flowers (or florets, as they are called in botanical terms) arranged into a dense head. Typical daisy flowers have two types of florets: disk florets, which form the flattened central part of the flower, and ray florets, which are found along the outer edge of the disk and form the 'petals' of the daisy. This species, however, does not have ray florets and therefore appears to have lost its petals! Around the base of each floret is a row of silky hairs (pappus) which become longer and thicker as the seeds develop, and gives older inflorescences a fluffy appearance. These silky hairs remain attached to the seeds and enable the seeds to be dispersed by wind.
In 1943, when the species was described, it was very common, and not being very charismatic was thereafter ignored and almost forgotten. No further herbarium specimens were collected after the 1940s, until 2003 when the last remaining populations of S. exuberans were found at a few sites that are all destined for urban and industrial development. The sandstone grasslands around Pietermaritzburg and Durban have largely disappeared under the pressures of agriculture and development and with it, its 'most characteristic feature' is now close to extinction. Senecio exuberans has been classified as Endangered according to the IUCN Red List criteria, and yet it is not currently formally protected in any nature reserves.
The continued survival of Senecio exuberans is at present entirely dependent on the goodwill of private landowners. It is crucial that developments proceed sensitively so as not to further impact on the remaining populations, and that the natural ecological processes of the habitat, especially periodic fires, be maintained.
Distribution and habitat
Sandstone grasslands occur on isolated sandstone plateaus between Kranskop and Port Shepstone in KwaZulu-Natal (Mucina & Rutherford 2006). These grasslands have a rich diversity of species, and many are endemic, which means that they can only be found in this unique habitat. Senecio exuberans is one such endemic, and grows in sandstone grasslands around Pietermaritzburg.
Derivation of name and historical aspects
Senecio is a widespread and large genus consisting roughly of 1 500 species, with about 300 found in South Africa, and commonly referred to as groundsels or ragworts. They occur in all sorts of growth forms, from annual herbs to climbers, interesting succulents, woody shrubs and even small trees. Senecios can be found in a wide variety of habitats, from aquatic to desert, and many species are serious weeds preferring disturbed areas. The name Senecio is derived from the Latin senex, which means old man, possibly referring to the fluffy hairs around the base of the florets, which calls to mind the white beard of an old man.
When Senecio exuberans is in the fruiting stage, the weight of the heads causes the inflorescence branches to bend over or droop. According to R. Allen Dyer, who described this species, these gracefully drooping branches gives the plant 'an abandoned and rather exuberant appearance' (Dyer 1943) and so the name exuberans was given.
Senecio exuberans is wel ladapted to fires. The grasslands in which it occurs often burn during the dry winter, and although the above-ground parts of the plant are burnt, it is able to resprout again from the rootstock, which is safely protected from fires as it is underground. Fires are actually very important in the life cycle of S. exuberans, as it stimulates new growth and flowering. However, as the sandstone grasslands have become more and more fragmented by development, smaller patches of grassland are not burnt as there is a great risk to neighbouring properties. This poses an additional threat to populations of S. exuberans remaining on small grassland fragments, as in the long-term these plants will stop producing seeds and therefore there will be no young seedlings to replace older plants as they die.
While many species of Senecio can be very weedy, actively colonizing disturbed habitats, this is not the case with S. exuberans. It grows only in pristine, undisturbed grasslands, and does not readily return to grasslands that have recolonized abandoned agricultural fields, or other disturbed areas.
Much still needs to be discovered about the ecology of Senecio exuberans. The pollinator is not known, but small beetles that have been observed on the flower heads may be responsible for pollination. Seeds are wind dispersed, but the conditions required for germination are not known.
Althoug many species of Senecio are used in traditional medicine, there are no records for S. exuberans. Many Senecio species are also poisonous to humans and livestock. Senecio poisoning in livestock is referred to as dunsiekte.
Growing Senecio exuberans
Senecio exuberans has not yet been introduced into cultivation (Glen 2002), but cultivation may be a means to save this species from extinction. The following guidelines are gathered from general information on how to grow Senecio species and may not necessarily apply exactly to S. exuberans.
Senecio species are generally quite easy to grow from seed. Sow seed in well-drained, sandy soils during spring. Keep well watered during the summer growing season, especially young seedlings. Mature plants may require less watering. As S. exuberans naturally grows in open grasslands, make sure that seeds are sown in a sunny position. The habitat of S. exuberans, sandstone grasslands, are naturally low in nutrients, therefore avoid the use of fertilizer.
Remember, do not remove plants from the wild and do not collect seeds from wild plants without a permit!
Acknowledgement: Peter Wragg is thanked for providing the photographs of Senecio exuberans used in this article, as well as information on the threatened status of this species.
- Dyer, R.A. 1943. Plantae novae africanae: Senecio exuberans. Journal of South African Botany 9: 124-126.
- Eliovson, S. 1973. South African wild flowers for the garden. MacMillan, Johannesburg.
- Glen, H.F. 2002. Cultivated plants of southern Africa. Botanical names, common names, origins, literature. Jacana, Johannesburg.
- Mucina, L. & Rutherford, M.C. (eds). 2006. The vegetation of South Africa, Lesotho and Swaziland. Strelitzia 19. South African National Biodiversity Institute, Cape Town.
- Trinder-Smith, T.H. 2003. The Levyns guide to the plant genera of the southwestern Cape. Contributions from the Bolus Herbarium 21. UCT, Cape Town.
- Watt, J.M. & Breyer-Brandwijk, M.G. 1962. The medicinal and poisonous plants of southern and eastern Africa. Livingstone, London.
Threatened Species Programme
Plant Type: Perennial
SA Distribution: KwaZulu-Natal
Soil type: Sandy
Flowering season: Early Summer
Flower colour: Yellow
Aspect: Full Sun
Gardening skill: Average