«DINTERIA No. 29:79-109 Windhoek, Namibia – May 2004 Plant species of the Sperrgebiet (Diamond Area 1) Antje Burke1 & Coleen Mannheimer2 P.O. Box ...»
DINTERIA No. 29:79-109 Windhoek, Namibia – May 2004
Plant species of the Sperrgebiet (Diamond Area 1)
Antje Burke1 & Coleen Mannheimer2
P.O. Box 90230, Klein Windhoek, Namibia, Tel: +264-61-223739, Fax: +264-61-227906,
National Botanical Research Institute of Namibia, P/Bag 13184, Windhoek, Namibia,
Tel: +264-61-2022012, email: email@example.com
Based on specimen records, published sources and own observations, an updated list
of plant species is presented for the Sperrgebiet, the southwestern corner of Namibia.
This area is in the transitional zone of winter and summer rainfall in Namibia and a remarkable 1038 species of flowering plants, 13 ferns and 22 mosses and their relatives occur. This comprises nearly 25% of the entire flora of vascular plants in Namibia and some 21% of the plant diversity of the Succulent Karoo Biome. We conclude that the Sperrgebiet is undoubtedly one of Namibia’s prime plant diversity hotspots.
Zusammenfassung Wir stellen hier eine neue Liste von Pflanzen vor, die im Sperrgebiet, dem südwestlichen Teil Namibias vorkommen. Diese Liste basiert auf Herbariumbelegen, veröffentlichter Literatur und unseren eigenen Beobachtungen. Eine bemerkenswerte Vielfalt von Arten – 1038 Blütenpflanzen, 13 Farne und 22 Moose und verwandte Arten – kommen in diesem Übergangsgebiet von Sommer- und Winterregen vor. Das sind beinah 25% der gesamten Flora des Landes und machen das Sperrgebiet damit eindeutig zu einem Diversitätszentrum von Pflanzen in Namibia.
Keywords: Mesembryanthemaceae, Namibia, species diversity, southern Namib, Succulent Karoo Biome Introduction The Sperrgebiet (Diamond Area 1) comprises Namibia’s section of the Succulent Karoo Biome (Rutherford 1997), a biodiversity hotspot of global significance (Myers et al. 2000). This northern-most tip of the Succulent Karoo Biome is postulated to be an area rich in plant species in Namibia (Maggs et al. 1998; Craven 2002). However, exactly how many species occur has been a matter of speculation for some time. In Burke & Mannheimer 1997, as part of a stratification of the area into floristic zones, Williamson published a species list with some 660 species of vascular plants (ferns and angiosperms).
Recognising the importance of the area, the National Botanical Research Institute of Namibia, in collaboration with various researchers, has since 1996 embarked on annual collecting trips during the main growing season (July-October), and systematically covered the area.
Not only has the collecting coverage been vastly improved since the publication of the earlier species list, but also many groups of taxa, most notably amongst the Mesembryanthemaceae, have since been substantially revised by a number of workers (e.g. Klak & Linder 1998; Hartmann 1998; 2002a and 2002b). Building onto Williamson’s (1997) work, an updated species list is now badly needed. Recently there has also been increasing interest in the area by exploration and mining companies on one hand, and conservation intitiatives on the other (e.g. Succulent Karoo Ecosystem Plan 2002). An updated record of the status quo regarding plant diversity hence provides a crucial baseline.
The aims of this paper are twofold:
(1) to present an updated account of plant species diversity in the Sperrgebiet and (2) to provide, as far as possible, a traceable record of the changes since the previous publication (Williamson 1997).
Methods Study area The study area covers the restricted Diamond Area 1 (Sperrgebiet) in south-western Namibia, an area which is positioned in the winter-summer rain transitional zone in Namibia. The area is arid, with annual mean rainfall ranging between some 20 mm near the coast to just about 60 mm in the eastern sections. A variety of landscapes comprising coastal dunes, sand plains, mobile dunes, gravel plains and rocky outcrops, inselbergs (isolated mountains rising above the plains) and mountains provide diverse habitats for plants to take a foothold (Burke 2003). Fog is an important moisture source in the entire area, although its frequency abates along a coast-inland gradient (Olivier 1995). The constantly strong, prevailing southerly winds are another important climatic variable to be reckoned with.
The vegetation comprises largely low leaf-succulent shrubs, which in most areas reach about 30 cm in height. The stem-succulent Euphorbia gummifera is a dominant species in many parts of the area. The eastern sand and gravel plains also support grassland (Burke 2003).
Dinteria 29 (2004) Plant species of the Sperrgebiet
Data preparation This species list is based on data from the Specimens Database of the Namibian National Botanical Research Institute (NBRI), the previous published species list (Williamson 1997), selected published literature (for those groups where major revisions were available) and own observations by the authors. For the purpose of this study the study area was defined based on quarter degree squares and included 41 quarter degree squares from 2615CA in the northwest to 2816BB in the southeast.
Towards the east, the following quarter degree squares formed the boundary:
2615DB, 2616CC, 2716AB, 2716AD, DA and DC. These were included. We excluded the northern extension of the Sperrgebiet into the Namib sand sea and the quarter degree square of Aus.
A complete list of all species of vascular plants, ferns, mosses and liverworts was compiled based on the sources above. We then screened the list for obvious mistakes in the records and database, updated taxonomic changes and used relevant literature (e.g. Van Zyl 2000; Venter 2000; Germishuizen & Meyer 2003) to cross-check dubious records. However, no comprehensive literature search was undertaken.
Species were eliminated from Williamson’s list (1997), if there were (a) no specimens lodged at PRE (National Herbarium, National Botanical Insitute, Pretoria, South Africa) or WIND (National Herbarium Namibia), (b) the species had not been observed by the authors and (c) closest distribution records from the literature and NBRI Specimens Database made it unlikely that this species would occur in the area.
The nomenclature largely follows Germishuizen & Meyer (2003), the exception being where a different practise is followed by the National Herbarium of Namibia (e.g. for Lavrania and Zygophyllum, Aloe dichotoma, Carissa haematocarpa and Pelargonium mirabile). These follow Craven (1999) and later taxonomic revisions of several groups (e.g. Van Zyl 2000).
Results and discussion The following 33 species listed by Williamson (1997) were eliminated, as there were no geographically close records or herbarium specimens to be found: Acanthopsis hoffmannseggiana, Argemone mexicana, Babiana torta, Bergia anagalloides, Bulbine frutescens, Chaetobromus dregeanus, Chlorophytum calyptrocarpum, Cleome monophylla, Commelina africana, Crassula atropurpurea var. watermeyeri, Diplachne fusca, Frankenia repens, Galenia hemisphaerica, Galenia sarcophylla, Helichrysum tinctum, Indigastrum burkeana, Kedrostis hirtella, Lachenalia zebrina, Lithops karasmontana, Lycium ferocissimum, Moquinella rubra, Oncosiphon piluliferum, Ornithogalum nanodes, Ornithogalum toxicarium, Ornithoglossum dinteri, Peliostomum virgatum, Polygala pygmaea, Salsola contrariifolia, Suaeda fruticosa, Tetragonia echinata, Tetragonia pillansii, Tetragonia sarcophylla and Tribulocarpus dimorphanthus.
Dinteria 29 (2004) 81 Burke & Mannheimer We have also excluded four species that are either of questionable taxonomic status at present (Opophytum aquosum) or that may occur in the area, but no voucher specimens were found (Brownanthus ciliatus subsp. ciliatus, Putterlickia pyracantha and Tylecodon aridimontanus).
The most common alien species recorded thus far are Argemone ochroleuca, Datura inoxia, Datura stramonium, Eucalyptus camaldulensis, Nicotiana glauca, Prosopis spp. and Ricinus communis. There are many more naturalised weedy, alien species, as indicated in Appendix 1. At present the majority of these only occur along the Orange River and near settlements.
In total, 1038 flowering plants, 13 ferns and 22 moss and liverwort species are now reported to occur in the Sperrgebiet. Compared to the previously recorded 660 vascular plants (angiosperms and ferns) this represents 391 new records, which is a nearly 60 percent increase from the previous list. Overall, the 1051 species represent
24.3 percent of the total flora of vascular plants in Namibia.
This constitutes 21.5 percent of the flowering plant diversity in the entire Succulent Karoo Biome based on Hilton-Taylor’s (1996) estimate of total plant diversity in this biome. This is fair portion of the biome’s plant diversity, considering that the Sperrgebiet land surface covers approximately 20 % of the Succulent Karoo Biome.
We conclude that the Sperrgebiet is a biodiversity hotspot unrivalled in Namibia, and also of great importance in the Succulent Karoo region.
Future collecting should particularly focus on taxa of doubtful status, such as the genus Salsola and geophytes, which are still poorly collected in many areas.
Acknowledgements We are indebted to staff of the National Botanical Research Institute for their relentless efforts to improve collecting coverage in this area, identifying plants and finally preparing and supplying the dataset from the Specimens Database. The Ministry of Environment and Tourism provided research permits. John Burke, Trygve Cooper, Patrick Lane and John Mannheimer provided logistic support on many field trips and Namdeb Diamond Corporation, particularly their Environmental and Security Departments, assisted with permit applications, transport and accommodation. We would like to thank them all.
References BURKE, A. 2003. A habitat management plan for the Sperrgebiet. Draft December 2003, Namibian National Biodiversity Programme, Windhoek, 121 pp.
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HILTON-TAYLOR, C. 1996. Patterns and characteristics of the flora of the Succulent Karoo Biome, southern Africa. In: Van der Maesen, L.J.E., Van der Burgt, X.M., Van Medenbach de Rooy, J.M. (eds.) The biodiversity of African plants, pp. 58-72. Kluwer Academic Publishers, Dordrecht.
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Appendix 1. Plant species recorded in the Sperrgebiet (* = alien). The species are organised phylogenetically according to the main phyla, subphyla and classes. Within these, families and species are organised alphabetically.
Bryophyta and Hepatophyta (mosses and liverworts) Aytoniaceae Plagiochasma rupestre (J.R. Forst. & G. Forst.) Steph. var. rupestre Bryaceae Bryum argenteum Hedw.
Fabroniaceae Ischyrodon lepturus (Taylor) Schelpe Fissidentaceae Fissidens rufescens Hornsch.
Funariaceae Funaria sp.
Goniomitrium africanum (Müll. Hal.) Broth.
Gigaspermaceae Chamaebryum pottioides Thér. & Dixon Grimmiaceae Grimmia laevigata (Brid.) Brid.
Grimmia pulvinata (Hedw.) Sm.
Leucoperichaetium eremophilum Magill Orthotrichaceae Orthotrichum diaphanum (Schrad. ex Brid.) Lindb.
Pottiaceae Barbula sp.
Crossidium spiralifolium Magill Pseudocrossidium crinitum (Schultz) R.H. Zander Syntrichia chisosa (Magill, Delgad. & L.R. Stark) R.H. Zander Syntrichia papillosa (Wilson) Jur.
Tortula atrovirens (Sm.) Lindb.
Tortula muralis Hedw.
Trichostomum brachydontium Bruch.
Weissia latiuscula Müll. Hal.
Ricciaceae Riccia argenteolimbata O.H. Volk & Perold Riccia cavernosa Hoffm. emend. Raddi
Pteridophyta (ferns) Aspleniaceae Asplenium cordatum (Thunb.) Sw.
Azollaceae Azolla filiculoides Lam.* Equisetaceae Equisetum ramosissimum Desf. subsp. ramosissimum Ophioglossaceae Ophioglossum polyphyllum A.Braun Pteridaceae Cheilanthes capensis (Thunb.) Sw.
Cheilanthes deltoidea Kunze Cheilanthes hastata (L.f.) Kunze Cheilanthes hirta Sw.
Cheilanthes kunzei Mett.
Cheilanthes namaquensis (Baker) Schelpe & N.C.Anthony Cheilanthes rawsonii (Pappe) Mett. ex Kuhn Cheilanthes robusta (Kunze) R.M. Tyron Pellaea calomelanos (Sw.) Link var.calomelanos
SpermatophytaAngiospermae (flowering plants)Monocotyledonae
Amaryllidaceae Ammocharis coranica (Ker Gawl.) Herb.
Ammocharis longifolia (L.) M. Roem.