Diplacorchis tenuior in sense of Pole-Evans, not of (Rchb.f.) Schltr. (misapplied name)
National Status
Status and Criteria
Critically Endangered A3c
Assessment Date
2015/03/17
Assessor(s)
L. von Staden, A.J. Hankey, L. Mills & D. Raimondo
Justification
This orchid was previously classified as Vulnerable in the Red List of South African Plants (Raimondo et al. 2009) due to a large number of historical records. However, since 2007 extensive field surveys have taken place to establish the current situation of this species. Surveys of all historical localities within Gauteng have failed to locate any surviving subpopulations except for one subpopulation of 117 plants near Krugersdorp. Surveys indicate that many of the historical recorded subpopulations in Mpumalanga have also gone extinct, and only three small subpopulations remain in Mpumalanga, all numbering fewer than 10 plants and not considered viable in the long term. Eighty percent of the Krugersdorp population is under housing development application, and all three subpopulations in the Mpumalanga area occur either on the edges of urban settlements or within mining sites, and they are all likely to be lost to development over the next 50 years. As a terrestrial geophytic orchid with a generation length of 20 years, a population reduction of more than 80% is projected to occur within the next 60 years.
Short, open grassland and wooded grassland, on sandy gravel overlying dolomite, sometimes also on quartzite, 1 000-1 705 m.
Threats
This species is severely threatened by ongoing habitat loss to urban expansion in Gauteng and Mpumalanga. In Gauteng, all known historical localities have been affected by extensive urban expansion in recent years, and it appears that this species is now locally extinct within Gauteng except for one remaining subpopulation near Krugersdorp. As Gauteng province is where this species has been recorded in most abundance, habitat loss within this province has caused a significant population reduction. The only known remaining subpopulation within Gauteng is currently threatened by development. Other confirmed subpopulations in Mpumalanga are in an area zoned for development (Middelburg subpopulation), on the outskirts of an informal settlement (Witbank subpopulation), and at a mining site near Oogies, all are in danger of extirpation within the near future.
Population
A comparatively large number of herbarium specimens, together with comments by orchid experts indicate that this species was formerly common within Gauteng province. A few scattered records from adjacent provinces indicate that this species also occurs outside of Gauteng, but that it is probably much rarer outside the province. Such disjunct locality records are typical of orchid distributions, and may be the result of long-distance dispersal of dust-like orchid seeds. It is not known whether such isolated subpopulations established through long-distance dispersal are viable in the long term or not. Thus far three of subpopulations found in Mpumalanga all number 10 plants or fewer, and none of these are likely to be long term viable populations. Surveys of historical localities in Limpopo are still needed to establish whether the species is still extant in this province. However the old collection records note that the orchid was rare and so it is unlikely that a large viable population exists in Limpopo. There have been no records from Limpopo for the past 24 years.
At present one living subpopulation of ± 117 plants is known to survive in Gauteng. This subpopulation was rediscovered in 2007 at the same site where J.P.H. Acocks recorded it in 1956. Several field surveys by municipal and provincial conservation officials over the years, plus dedicated searches by orchid experts while researching a recently published book on orchids of the northern provinces of South Africa (McMurtry et al. 2009), plus a survey of all known historical localities within Gauteng between 2010 and 2015 in the correct flowering season of this orchid have failed to locate any other surviving subpopulations in Gauteng. After extensive surveys in Mpumalanga three subpopulations are known, the Middelburg subpopulation numbering 10 plants, a subpopulation just outside of Witbank numbering 8 plants and 10 plants from a mining site near Oogies.
As this orchid is not closely associated with any particular vegetation type, and its habitat requirements are not well understood, it is difficult to estimate population reduction based on habitat loss. Population reduction is therefore estimated based on loss of known localities in the past. We estimate a population reduction of 55-70% in the past 60 years (generation length 20 years) due to habitat loss mainly to urban expansion. Future reduction in the population is estimated on the four confirmed populations. Eighty percent of the only viable subpopulation from Krugersdorp is under development application. All of the Mpumalanga subpopulations will be lost in the next 50 years to development. This equates to an overall loss of 80% of the population over the next 60 years (three generations, the standard generation length used for geophytic orchids).
Population trend
Decreasing
Conservation
No known living subpopulations of this orchid are currently protected in any formal conservation area. As per SANBI�s recommendations for the mitigation of habitat loss to threatened species (Driver et al. 2009) we recommend no further loss of habitat until such time as another viable subpopulation of this orchid can be found. Formal protection in terms of the National Environmental Management: Protected Areas Act (Act 57 of 2003) is recommended for the only currently known extant subpopulation.
Driver, M., Raimondo, D., Maze, K., Pfab, M.F. and Helme, N.A. 2009. Applications of the Red List for conservation practitioners. In: D. Raimondo, L. Von Staden, W. Foden, J.E. Victor, N.A. Helme, R.C. Turner, D.A. Kamundi and P.A. Manyama (eds). Red List of South African Plants. Strelitzia Strelitzia 25:41-52. South African National Biodiversity Institute, Pretoria.
Linder, H.P. and Kurzweil, H. 1999. Orchids of southern Africa. A.A. Balkema, Rotterdam.
McMurtry, D., Grobler, L., Grobler, J. and Burns, S. 2008. Field guide to the Orchids of northern South Africa and Swaziland. Umdaus Press, Hatfield.
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.
Summerhayes, V.S. 1955. A revision of the genus Brachycorythis. Kew Bulletin 10:244-245.
Citation
von Staden, L., Hankey, A.J., Mills, L. & Raimondo, D. 2015. Brachycorythis conica (Summerh.) Summerh. subsp. transvaalensis Summerh. National Assessment: Red List of South African Plants version . Accessed on 2025/04/18
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