Worcester Silkypuff

Taxonomy
Scientific Name
Diastella parilis Salisb. ex Knight
Higher Classification
Dicotyledons
Family
PROTEACEAE
Common Names
Worcester Silkypuff (e)
National Status
Status and Criteria
Critically Endangered A4ace
Assessment Date
2019/08/12
Assessor(s)
A.G. Rebelo, D. Raimondo, L. von Staden & H. Mtshali
Justification
Diastella parilis is a range-restricted and localized habitat specialist, that now persists within a very small area in the Breede River Valley, after extensive historical habitat loss to agricultural expansion. It was still relatively common in remaining alluvium fynbos remnants in the early 1990s, but ongoing vineyard expansion reduced the population by at least 55% since then, and as population decline is expected to continue at a similar rate, population reduction is projected to exceed 80% within three generations. Only four subpopulations remain, and none of these are formally protected.
Distribution
Endemism
South African endemic
Provincial distribution
Western Cape
Range
This species is endemic to the Breede River Valley in the Western Cape, where it occurs in a small area on the alluvial flats between the Slanghoek Mountains and the Breede River north of Rawsonville.
Habitat and Ecology
Major system
Terrestrial
Major habitats
Breede Alluvium Fynbos
Description
It is endemic to Breede Alluvium Fynbos, where it is localized to seasonally damp places. Mature individuals are killed by fires, and only seeds survive. Seeds are released after ripening, and dispersed by ants to their underground nests, where they are protected from predation and fire. It is pollinated by insects.
Threats
The most severe threat to this species is habitat loss to vineyard expansion. More than 70% of its habitat is already irreversibly modified, and rapid, ongoing loss has been observed over the past 24 years. It is dependent on seasonally damp sites, but drainage and canalization of the Breede River floodplain is diverting water flow from many small remaining habitat fragments. Furthermore, fire exclusion and alien invasive plants are causing ongoing degradation of remaining habitat remnants.
Population

The population of Diastella parilis has been fragmented due to extensive habitat loss to vineyards. Protea Atlas Surveys recorded six remaining subpopulations in the early 1990s, and three of these numbered several thousand individuals, with the population size estimated to be around 14 000 mature individuals. Since then, two subpopulations were entirely extirpated due to loss to vineyard expansion, and frequent monitoring recorded continuing decline in three others. The largest subpopulation was at two adjacent farms Grootvlakte and Wysersdrift, and consisted of a few thousand plants over a 4 km stretch of alluvium fynbos. More than 50% of this subpopulation was lost to vineyard expansion over the past two decades, with remaining fragments in poor condition due to alien plant infestations and destructive infrastructure developments such as the installation of pipelines (N.A. Helme pers. comm.). Another large subpopulation on the farm Rustfontein north of the Badsberg consisted of several thousand plants in 1994, but has been reduced by 40% due to vineyard expansion since then. A smaller subpopulation of several hundred plants occurred on the adjacent farm Driefontein, but this entire subpopulation was lost to vineyard expansion. At Witelsrivier at the foot of the Slanghoek Mountains there is a subpopulation of about 700 plants. Regular monitoring between 1999 and 2015 indicates that it is remaining stable. The site was proposed for conservation stewardship, but the landowner is not interested (R. Koopman, pers. comm. 2019). Another smaller fragment on the adjacent farm Kleingeluk had a few hundred plants in 1994. Part of the subpopulation was lost to vineyard expansion, with only 80 plants remaining in a 10 hectare area in 2003, but no further loss has been recorded since. A subpopulation on the farm Tweeheuwels numbered around 2250 plants in 1994, but this entire subpopulation was lost to vineyard expansion since then. The current population size is estimated to number around 6300 plants, thus there has been a 55% population reduction observed in the past 24 years. If the observed rate of population decline is to continue, population reduction will exceed 80% by 2030, which is within three generations for this species. As it is a reseeder, generation length is linked to fire cycles, which under natural conditions is 15-20 years. Historical records suggest that the species formerly occurred further north up the Breede River Valley as far as Tulbagh Waterfall, but no remaining subpopulations could be relocated during Protea Atlas Project surveys, and it is assumed to be locally extinct in this area.


Population trend
Decreasing
Assessment History
Taxon assessed
Status and Criteria
Citation/Red List version
Diastella parilis Salisb. ex KnightCR B1b(i,ii,iii,iv,v)c(iv)Raimondo et al. (2009)
Diastella parilis Salisb. ex KnightVulnerable Hilton-Taylor (1996)
Diastella parilis Salisb. ex KnightRare Hall et al. (1980)
Bibliography

Goldblatt, P. and Manning, J.C. 2000. Cape Plants: A conspectus of the Cape Flora of South Africa. Strelitzia 9. National Botanical Institute, Cape Town.


Hall, A.V., De Winter, M., De Winter, B. and Van Oosterhout, S.A.M. 1980. Threatened plants of southern Africa. South African National Scienctific Programmes Report 45. CSIR, Pretoria.


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.


Rebelo, T. 2001. Sasol Proteas: A field guide to the proteas of southern Africa. (2nd ed.). Fernwood Press, Vlaeberg, Cape Town.


Citation
Rebelo, A.G., Raimondo, D., von Staden, L. & Mtshali, H. 2019. Diastella parilis Salisb. ex Knight. National Assessment: Red List of South African Plants version 2020.1. Accessed on 2020/09/30

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Distribution map

© N.A. Helme

© N.A. Helme

© C. Paterson-Jones


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