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Euphorbia knobelii

Taxonomy
Scientific Name
Euphorbia knobelii Letty
Higher Classification
Dicotyledons
Family
EUPHORBIACEAE
Synonyms
Euphorbia perangusta R.A.Dyer
National Status
Status and Criteria
Endangered A2ace; B1ab(iii,v)+2ab(iii,v)
Assessment Date
2016/09/27
Assessor(s)
R.H. Archer, L. von Staden, J.E. Victor & N. Hahn
Justification
A population reduction of 50-60% is estimated based on field observations over a period of 30 years (less than three generations). Plants remain at two to five locations within a restricted area (EOO 1277 km²), and continue to decline due to habitat degradation and disease.
Distribution
Endemism
South African endemic
Provincial distribution
North West
Range
Marico district north of Zeerust.
Habitat and Ecology
Major system
Terrestrial
Major habitats
Dwarsberg-Swartruggens Mountain Bushveld
Description
Woodland and thornveld, wedged among large rocks on the slopes of quartzitic ridges, 1000-1200 m.
Threats
Illegal collection of wild plants has severely reduced the subpopulations at the type localities for both E. perangusta and E. knobelii, leading to the local extinction of the subpopulation at the type locality for E. knobelii. The most severe threat that is impacting subpopulations across the range is severe habitat degradation and trampling by livestock. Plants are not browsed, but stems are damaged by trampling making plants more susceptible to disease and fungal infections, and is drastically reducing the ability of mature individuals to reproduce. Severe droughts in the 1980s and early 1990s may also have marred the ability of the population to recover from disease-related die-off (Hahn 2013). During drought years, porcupines have been noted to feed on subpopulations of E. perangusta, destroying large proportions of already very small subpopulations. Poor recruitment is a cause for concern, most plants are old and no seedlings was noted during monitoring in the 1980s (Raal 1988).
Population

The population of E. knobelii/perangusta was monitored as part of a plant conservation programme in the 1980s. Surveys of the habitat recorded 253 plants in five subpopulations, with the largest subpopulation consisting of 128 plants, the others between 4 and 50 mature individuals (Raal 1988). The largest subpopulation declined to between 30-40 mature individuals by 1998 (Peckover 1999), and the total population was estimated to be less than 100 mature individuals in 1998 (Peckover 1999). Significant declines were also observed at the type locality of E. knobelii, where there were less than 10 plants remaining by 2008 (A. Barac pers. comm. 2008), and no plants could be found there in 2011 (Hahn 2013). Follow-up surveys in 2011 found the southernmost subpopulations to be stable. Four additional subpopulations found in the area however showed severe die-off and were all on the brink of extinction (Hahn 2013). Based on monitoring data, a population reduction of 50-60% is estimated within the past three generations (generation length 10-20 years). Ongoing monitoring is needed to determine the long-term effects of drought and parasites on the dynamics of the wild population (Hahn 2013).


Population trend
Decreasing
Notes
This assessment includes plants described under the name Euphorbia perangusta R.A.Dyer. E. perangusta overlaps in range with E. knobelii and is insufficiently distinct from E. knobelii to warrant recognition as a separate taxon (R.H. Archer pers. comm. 2008).
Citation
Archer, R.H., von Staden, L., Victor, J.E. & Hahn, N. 2016. Euphorbia knobelii Letty. National Assessment: Red List of South African Plants version 2017.1. Accessed on 2019/12/11

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Distribution map


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