Bastard quiver tree (Aloe pillansii)
|Size||Height: up to 10 m (2)|
The bastard quiver tree is classified as Critically Endangered (CR) on the IUCN Red List (1), and listed on Appendix I of CITES (3).
The bastard quiver tree (Aloe pillansii) casts a dramatic shape on the desolate skyline of the Succulent Karoo in southern Africa. This succulent tree can be up to ten metres tall; there are only a few branches high up on the trunk and reaching skywards, whilst the leaves tend to droop down (2). The bark is pale and smooth, often flaking off in large sections (2). The bright yellow flowers are produced on branched inflorescences that are located below the leaf rosettes (2).
The bastard quiver tree found mainly in the Richtersveld region of the Northern Cape Province of South Africa, reaching north into southern Namibia (1).
The bastard quiver tree is mainly confined to intensely hot and arid areas of the Succulent Karoo biome which receive winter rainfall which may be supplemented with fog precipitation (2) (4). It grows on rocky, gravel slopes of mountain summits and occasionally on sandy plains (4).
Little is known about the reproductive biology of the bastard quiver tree (5), but the species’ flowers appear in early summer (around October) (2), and their structure suggests that they may be pollinated by sunbirds (5). If this is the case, then the bastard quiver tree is one of very few species in the area that is bird-pollinated and therefore plays a key role within the ecosystem (5).
These trees are a keystone species of this region; many animals rely on their existence for a variety of different reasons (5). It is one of very few high points in this desolate vegetation that can act as a vantage point for birds of prey and as nesting sites for other birds. The succulent nature of the leaves and flowers is also an important source of moisture for a range of different animals (5).
Due to the absence of growth rings in this monocot species, it is very difficult to tell how long the bastard quiver tree lives. It is suspected, however, that they grow very slowly and live between 250 and 350 years (6).
Recent surveys of the bastard quiver tree in the Richtersveld region of the Northern Cape Province of South Africa, as well as in Namibia, suggest that there has been very little successful reproduction in the last 100 years. In addition, many of the older trees are dying, indicating that the population does not appear to be naturally regenerating (5) (7). The rarity of the bastard quiver tree may be partly attributed to their habitat; in harsh environments the problems of survival are amplified (5). Similar declines in population regeneration in sister species Aloe dichotoma, (the quiver tree), have been attributed to climate change (8) and it is very likely that the bastard quiver tree is being affected similarly. These effects are worsened by the removal of plants by horticultural collectors, as well as through herbivory by baboon, porcupines, rock rabbits and livestock, which also trample young plants (4) (5) (7). Populations may also be affected by damage caused by leaf scale insects, and by base metal mining in Namibia (9).
Bastard quiver trees are protected in South Africa and Namibia (10), and are listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), effectively banning international trade in wild plants of this species (1). Further research into this important species is vitally needed, together with the careful monitoring of existing populations (5). Bastard quiver trees are a vital component of the Succulent Karoo ecosystem and an important tourist draw to the region, thus making conservation efforts imperative for the area.
For further information on the Succulent Karoo ecosystem and its conservation:
Succulent Karoo Ecosystem Programme:
Authenticated (26/11/07) by Wendy Foden, Programme Officer: Climate Change, IUCN Species Programme.
- Inflorescences: the reproductive shoot of the plant, which bears flowers.
- Succulent karoo: a biome, (a major regional or global living community), primarily determined by the presence of low winter rainfall and extreme summer aridity. The vegetation is dominated by dwarf, succulent shrubs, and once each year, during the spring, mass flowering displays occur.
IUCN Red List (March, 2011)
- Coates Palgrove, K. (1977) Trees of Southern Africa. C. Struik Publishers, Cape Town.
CITES (March, 2003)
- Loots, S. (2005) A Red Data Book of Namibian Plants. SABONET Report No. 38, Namibia.
- Midgley, J.J., Cowling, R.M., Hendricks, H., Desmet, P.G., Esler, K. and Rundel, P. (1997) Population ecology of tree succulents (Aloe and Pachypodium) in the arid western cape: decline of keystone species. Biodiversity and Conservation, 6: 869 - 876.
- Foden, W. (2007) Pers. comm.
- Swart, E. and Hoffman, M.T. (2006) The population status of Aloe pillansii L. Guthrie in Southern Namibia. Report to the Department of Environment and Tourism, Kimberly.
- Foden, W.B., Midgley, G.F., Hughes, G., Bond, W.J., Thuiller, W., Hoffman, M.T., Kaleme, P., Underhill, L.G., Rebelo, A. and Hannah, L. (2007) A changing climate is eroding the geographic range of the Namib Desert tree Aloe through population declines and dispersal lags. Diversity and Distributions, 13: 645 - 653.
- Golding, J. (2002) South African Plant Red Data Lists. Southern African Botanical Diversity Network Report No. 14. SABONET, Pretoria.
- Oldfield, S. (1997) Cactus and Succulent Plants – Status Survey and Conservation Action Plan. IUCN/SSC Cactus and Succulent Specialist Group. IUCN, Gland, Switzerland and Cambridge, UK.