Pondo Weeping Thorn

Taxonomy
Scientific Name
Colubrina nicholsonii A.E.van Wyk & Schrire
Higher Classification
Dicotyledons
Family
RHAMNACEAE
Common Names
Pondo Weeping Thorn (e)
National Status
Status and Criteria
Vulnerable D1+2
Assessment Date
2007/10/12
Assessor(s)
L. von Staden, J.E. Victor & A.E. van Wyk
Justification
Known from about 200 individuals in the wild, however, more subpopulations are being discovered. This species grows in secluded, inaccessible gorges and it is very likely that there are a few undiscovered subpopulations, especially in the light of significant range extensions brought about by recent discoveries of new subpopulations. We estimate that there are more than 250 mature individuals but fewer than 1 000. AOO of this habitat specialist is estimated as <20 km², and it is potentially threatened by alien plant invasion at four locations. Poor recruitment is a concern, but healthy subpopulations are presently maintained by vegetative reproduction and there is no current evidence of continuing decline.
Distribution
Endemism
South African endemic
Provincial distribution
Eastern Cape, KwaZulu-Natal
Range
Between Port St Johns and the Umtamvuna River. Isolated occurrences as far north as the uMzinto district (KwaZulu-Natal) and as far south as the Kentani district (Eastern Cape).
Habitat and Ecology
Major system
Terrestrial
Major habitats
Scarp Forest
Description
Scarp forest. Climax riverine forest, close to, and usually overhanging the water, 100-400 m.
Threats
C. nicholsonii occurs on stream banks deep inside scarp forests and gorges, and is unlikely to be affected by forest destruction due to the inaccessibility of the habitat (T. Abbott pers. comm.). This sub-canopy tree appears to prefer stream banks and areas where there is light filtering through sparse areas in the forest canopy (Boon 2001), the type of light conditions that is also preferred by the most serious alien invasives of forest systems in South Africa Chromolaena odorata (triffid weed), Lantana and Solanum mauritianum (bugweed). Alien encroachment is potentially threatening subpopulations in the Vernon Crookes Nature Reserve (Boon 2001) as well as on the banks of the Mtentu (K. van der Walt pers. obs.) C. nicholsonii could potentially decline as a result of lack of fruit set and therefore recruitment, however, at present healthy subpopulations appear to be maintained by means of vegetative reproduction (D. Styles pers. comm.). However, if wildfire were to impact on any of the C. nicholsonii subpopulations, a subpopulation could be entirely devastated with no potential of regeneration from soil stored seed banks (Boon 2001).
Population

Subpopulations are generally very small, consisting of no more than 10 individuals, except on Mount Sullivan, where there is about 20-30 mature individuals (T. Abbott pers. comm.) The Daza River subpopulation consists of ± 15 plants (notes on Abbott, A. 2552, 23-3-1985, NH). Three subpopulations in Vernon Crookes have respectively 15-20, 30 and 50 mature individuals (Boon 2001, D. Styles pers. comm.).


Population trend
Stable
Conservation
Protected in the Vernon Crookes, Umtamvuna, Mkambati and Silaka Nature Reserves.
Notes
There is only one other species of Colubrina indigenous to Africa, C. asiatica var. asiatica which is a widespread littoral shrub that is dispersed by ocean currents. C. nicholsonii is however not a littoral species and it is unlikely to have recently reached the Pondoland region through long distance sea dispersal. In stead, it is thought to be one of a group of palaeoendemics found in the Pondoland Centre. Other evidence that points to palaeoendemism is the discontinuous distribution, poor reproduction and the fact that Colubrina is considered the evolutionary most 'primitive' genus of the Rhamnaceae (Van Wyk and Schrire 1986). Many of these Pondo-palaeoendemics are slowly declining due to poor reproductive capabilities and are thought to be on the brink of natural extinction (Van Wyk and Schrire 1986).
Assessment History
Taxon assessed
Status and Criteria
Citation/Red List version
Colubrina nicholsonii A.E.van Wyk & SchrireVU D1+2Raimondo et al. (2009)
Colubrina nicholsonii A.E.van Wyk & SchrireEN Scott-Shaw (1999)
Colubrina nicholsonii A.E.van Wyk & SchrireRare Hilton-Taylor (1996)
Bibliography

Boon, R. 2001. The (re)-discovery of the Pondo Snakewood, Colubrina nicholsonii, in KwaZulu-Natal. PlantLife 25:17-19.


Boon, R. 2010. Pooley's Trees of eastern South Africa. Flora and Fauna Publications Trust, Durban.


Hilton-Taylor, C. 1996. Red data list of southern African plants. Strelitzia 4. South African National Botanical Institute, Pretoria.


Raimondo, D., von Staden, L., Foden, W., Victor, J.E., Helme, N.A., Turner, R.C., Kamundi, D.A. and Manyama, P.A. 2009. Red List of South African Plants. Strelitzia 25. South African National Biodiversity Institute, Pretoria.


Scott-Shaw, C.R. 1999. Rare and threatened plants of KwaZulu-Natal and neighbouring regions. KwaZulu-Natal Nature Conservation Service, Pietermaritzburg.


Van Wyk, A.E. and Schrire, B.D. 1986. A remarkable new species of Colubrina (Rhamnaceae) from Pondoland. South African Journal of Botany 52(4):379-382.


Citation
von Staden, L., Victor, J.E. & van Wyk, A.E. 2007. Colubrina nicholsonii A.E.van Wyk & Schrire. National Assessment: Red List of South African Plants version 2017.1. Accessed on 2018/11/21

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Distribution map

© R. Boon

© R. Boon

© R. Boon

© G. Grieve


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