The grasslands and wetlands of the Sekhukhuneland Centre of Plant Endemism , South Africa

A hierarchical classification, description, and ecological and floristic interpretations are presented on the vegetation types of the grasslands and wetlands of the Sekhukhuneland Centre of Plant Endemism. Relevés were compiled in 74 stratified random plots. A TWINSPAN classification, refined by Braun-Blanquet procedures, revealed eight associations. 11 subassocia­ tions and four variants. Many new syntaxa are described and ecologically interpreted. For each syntaxon. the species richness, endemism and conservation status was determined. The floristic and habitat information, proposed classification, general description and vegetation key are provided to aid future identification of conservation areas, land use planning and further research. An ordination (DECORANA). based on floristic data, confirmed the relationships that exist between plant commu­ nities and associated habitats and environmental gradients. Much of the plant community diversity and distribution can be ascribed to a heterogeneous environment, predominantly determined by soil moisture.


INTRODUCTION
Several phytosociological studies have been conducted on vegetation types along the northeastern escarpment of the Northern Province and Mpumalanga (Bloem 1988;Deall et al. 1989;Matthews et al. 1992a. b;Burgoyne et al. 2(XX)).However, the vegetation of some areas still remains to be investigated and described, both on recon naissance level and in more detail.The undulating norite hills in the Roossenekal-Tonteldoos region is an area with very limited information on the vegetation.It is located in the southern portion of the Sekhukhuneland Centre of Plant Endemism (SCPE) (Van Wyk & Van Wyk 1997;Van Wyk & Smith 2001), and comprises the Roossenekal Subcentre of Endemism (Siebert 1998).The Roossenekal Subcentre is known for its many plant endemics, the dis tributions of which correlate with the diversity in geologi cal substrate in the region (Siebert 1998;Siebert et al. 2001).
Only Acocks (1988) accurately mapped the high-altitude outcrops of norite (Leolo Mountains) in the north ern region of the SCPE as grassland, namely North-east ern Sandy Highveld (57).Geologically and floristically the Leolo Mountains is similar to the Roossenekal Subcentre, and is treated as part of the study area covered in this paper (Siebert 1998).However, the vegetation classification of the entire Sekhukhuneland Centre needs further attention, as comparatively little is known about its plant communities, floristic diversity and the relation ship between distribution patterns of plants and the clayey soils derived from the ultramafic norite.This paper forms part of a comprehensive vegetation and floristic survey of the Sekhukhuneland area.It is envisaged that the identification, classification and description of the various vegetation units (syntaxa) will contribute to the knowledge of the plant diversity and biological intricacies of the region.This paper provides ecological and floristic data of the region's grasslands and wetlands, and the associated habitats, by characteriz ing and interpreting the vegetation units.Classification is basic to the formulation of a management policy and for proper land use planning.An assessment of the plant species richness, endemism and Red Data List taxa in the plant communities of the study area is supplied as base line data to apply in future conservation actions in the region and application in ecosystem management.An adequate database of natural features and other land uses is essential for effective land use management and imple mentation (Kent & Ballard 1988;Bedward et al. 1992;Rhoads & Thompson 1992).
In a broad overview of the vegetation types of the SCPE.Siebert et al. (2002) recognized six major vege tation units.The vegetation units described in this paper cover the Themeda triandra-Senecio microglossus Cool Moist Grassland and the Fuirena pubescens-Schoenoplectus corymbosus Wetland Vegetation, the two major vegetation types of the relatively moist Roossenekal Subcentre.A vegetation key is presented to aid with the identification of the proposed syntaxa in the study area.

STUDY AREA
The study area is situated in northern Mpumalanga between latitude 25° 00 ' and 25° 20' S and longitude 29° 50' and 30° 05' E (southern part of the SCPE) and southern Northern Province between latitude 24° 30' and 24° 50' S and longitude 30° 00' and 30° 05' E (Leolo Mountains) (Figure 1).The area covers ± 1 500 km2 and comprises a homogeneous geology (Visser et al. 1989), with a heterogeneous physiography (Land Type Survey Staff 1987).The Sekhukhuneland Centre is more or less restricted to the Rustenburg Layered Suite of the Bushveld Complex (Siebert et al. 2001).The area dealt with in this paper lies on the Upper and Main Zones of the Rustenburg Layered Suite and is mainly underlain by concentric belts of norite, and to a lesser degree outcrops of ferrogabbro (Visser et al. 1989).This norite stratum extends northsouth and rises to form the Leolo Mountains (1 700 m asl).The lower reaches of the mountainous areas are character ized by many small outcrops of magnetite.
The Roossenekal Subcentre is defined as the grassland areas in and adjacent to the sixteenth degree grid 2529 BB and also includes the outlier Leolo Mountains in the Northern Province.Thirty-four of the Sekhukhuneland endemics/near-endemic plant species which are largely restricted to these areas were recorded during the study (Siebert 1998).The area forms an ecotone between the Mixed Bushveld (18) and the North-eastern Sandy Highveld (57) Veld Types (Acocks 1988), but it is proba bly more representative of Bankenveld (61), than any of the aforementioned veld types.The valleys have a sub tropical climate with little or no frost in winter, whereas in the mountains, conditions become more temperate with increasing altitude.In this region of undulating rocky hills, the vegetation is characterized by scattered woodlands in sheltered habitats of footslopes and in valleys, and grass land with bush clumps covering the exposed plateaus, hill slopes and valleys.The difference in altitude between the two most extreme locations is ± 500 m (1 700 m asl on the Leolo Mountains to 1 200 m asl where the Klip River cuts through the hills near Roossenekal).
The study area lies in the summer rainfall region, with an average annual precipitation of about 700 mm (South African Weather Bureau 1998).Local rainfall patterns are strongly influenced by the area's topography and alti tude (Siebert 1998), varying from 721 mm in the east, to 607 mm per annum in the west; 710 mm in the south, to 702 mm in the north (Erasmus 1985).Daily average tem perature ranges from a minimum of 2.8°C in winter to a maximum of 25.9°C in summer, with an average annual temperature of 16.2°C (South African Weather Bureau 1998).Temperatures vary at different localities within the area, also correlating strongly with physiographic regions, being higher in low-lying valleys and lower on high-lying plateaus (Buckle 1996).However, minimum temperatures of below freezing point are rare, even in the high-lying areas.

METHODS
A first approximation of a vegetation classification, based on the total floristic data set of 415 stratified ran dom sample plots was obtained by the application of the Two-Way Indicator Species Analysis (TW1NSPAN) (Hill 1979a).The first step of an objective multivariate classification identified six major vegetation types for the Sekhukhuneland Centre (Siebert et al. 2002).These results were then used to subdivide the data set into five phytosociological tables.One of these tables, represent ing two major vegetation types, namely grasslands and wetlands, was again subjected to TW1NSPAN.Using Braun-Blanquet procedures in the MEGATAB computer program (Hennekens 1996a), we further refined the resultant classification.
Floristic and habitat data of the grasslands and wetlands were derived from 74 relevés.Stratification was based on terrain type, aspect and vegetation structure.To standardize the plot size and to counter the bias of different scale (Jonsson & Moen 1998), plots sampled in the grassland were fixed at 100 m2.Within each sample plot, all species were recorded and a cover-abundance value was assigned to each species according to the Braun-Blanquet scale (Mueller-Dombois & Ellenberg 1974).Plant species names conform to those of Retief & Herman (1997), and the practice followed in the H.G.W.J. Schweickerdt Herbarium (PRU), University of Pretoria.Terminology to describe vegetation structure follows Edwards (1983).Environ mental data recorded for each sample plot include terrain type (Land Type Survey Staff 1987), aspect, slope, geolo gy (Visser et al. 1989), soil type (MacVicar et al. 1991) and rockiness of soil surface.Longitude and latitude readings were also recorded for each sample plot using a GPS.All relevé data are stored in the TURBOVEG database (Hennekens 1996b), managed by the Department of Botany, University of Pretoria (Mucina et al. 2000).Syntaxa names are given in accordance with the Code of Phytosociological Nomenclature (Weber et al. 2000).
The ordination algorithm Detrended Correspondence Analysis (DECORANA) (Hill 1979b) (Figure 2) was applied to confirm gradients in vegetation and the rela tionship between these plant communities and the phys ical environment.
To facilitate the identification of areas of high conser vation potential, the alpha diversities of the different plant communities were calculated.The alpha diversity (plant species richness) is defined as the number of species per unit area within a homogeneous community or the total number of species per community (Whittaker 1977).A 100 m2 sample plot was taken as the unit area within a homogeneous community.
The geographical distribution of all the taxa was ver ified at the National Herbarium (PRE).Pretoria, to iden tify any taxa endemic/near-endemic to the region (Siebert 1998).All taxa were also checked against the Red Data List of southern African plants (Hilton-Taylor 1996) to determine their conservation status.

Classification o f vegetation
The analysis resulted in the identification of 17 plant communities, ordered as eight associations, 11 subassoci ations and four variants (Table la, b).These units were subsequently hierarchically classified.Since the study area covered by these communities lies in the climatical ly uniform moist and cool southern region of the SCPE (Siebert 1998), no major macroclimatic variation plays a role in local differentiation of the plant communities.The major plant communities relate to soil character, rocki ness and terrain type, with aspect and slope also playing minor roles.Communities were not always distinctive in the field.This might be attributed to the homogeneity of grassland physiognomy and the heterogeneity of the envi ronmental factors, which resulted in a complex mosaic distribution pattern of habitats and associated vegetation.
The hierarchical classification of the vegetation rein forces the correlation between habitat and plant commu nities (Figures 2, 3).The distribution of the SCPE endemic/ near-endemic and Red Data List plant taxa among vari ous plant communities is listed in Table 2.A summary of selected floristic and habitat attributes for each plant community is supplied in Table 3.

Description o f plant communities
The Themeda triandra-Senecio microglossus Cool Moist Grassland and scattered Fuirena pubescens-Schoenoplectus corymbosus Wetland Vegetation are pre dominantly restricted to the valleys, slopes and plateaus of undulating norite hills (Siebert et al. 2002).Surface rocks are common and abundant in many of the commu nities, with soil clay percentages varying from 25% to more than 50%.The vegetation can be classified into herbland and grassland (Edwards 1983).An important feature of the region is the fact that the mountain and hill ranges have a north-south orientation; therefore the grassland communities are mostly restricted to eastern and western aspects, crests and valleys.Grasslands have been a long-standing component of the Afromontane vegetation mosaic (Meadows & Linder 1989;Matthews et al. 1993), and are therefore seen as primary vegeta tion.Plant communities of the grasslands and wetlands recognized in the SCPE are classified as follows: Environmental data: a medium altitude grassland, forms a transition from low to high altitude ( I 700 m asl).It lies in a rather moist region (> 6(X) mm/annum), most ly restricted to the summit of the Leolo Mountains on norite.The habitat is a gentle undulating plateau (1-5°) with a general east-west aspect (Table 3).The dominant

Zantedeschio pentlandi-Aloetum castaneae ass. nova hoc loco
Nomenclatural type: relevé 100 (holotypus) Environmental data: a short herbland on rocky flats, areas where bedrock is exposed at ground level.The plant community is associated with rock outcrops of norite, a rock type mined extensively as dimension stone in the region.It is situated on gentle slopes (0-5°) and with a very high surface rock cover of 50-70% (Table 3).Solid exposed rock sheets can cover areas of 25 m2.The dominant soil type is the Mispah Form, indicating very shallow soils over hard rocks, often restricted to crevices.The habitat is situated on the midslopes, scarps and crests of undulating hills.Floristic diversity: this association exhibits a typical floristic relationship with other grasslands of the SCPE (Table la).The average number of species encountered per sample plot is 36, with 105 species the total number recorded for the association (five relevés) (Table 3).Fifteen taxa of conservation significance are present in the association (Table 2), five are SCPE endemics, six are SCPE near-endemics and seven are Red Data List taxa.This association has a high number of plant taxa with conservation status in the southern region of the SCPE.The association also has a high number of plant taxa with conservation status restricted to it, such as Asclepias sp.(Siebert 27) (endemic), Eucomis montana (Rare), Xerophyta retinervis form (endemic) and Zantedeschia pentlandii (endemic, Rare).
Environmental data: short, dense grassland associated with plateaus or terraces on rocky undulating hills.The association is found on all aspects, on gentle to moderate slopes (5-15°) of footslopes, midslopes, scarps and crests (Table 3).Soils are characterized by a melanic Ahorizon underlain by hard rock (Miikwood Form) or a soft carbonate horizon (Steendal Form).Rock cover is 15-75% and rock diameter 0.1-1 m (Table 3).
Diagnostic and dominant/prominent taxa: character istic species of the association are represented by species group C (   Floristic diversity: the average number of species encountered per sample plot in this association is 48, with the total number of plant species being a minimum of 119 taxa (29 relevés) (Table 3).There are 25 plant taxa of conservation value in the association, of which four are restricted to it.These include taxa such as the near endemics, Argyrolobium wilmsii and Pachy carpus transvaalensis (Table 2).Red Data List taxa include Callilepis leptophylla (status is Rare in KwaZulu-Natal), Melhania randii (status is Insufficiently Known in the northern provinces) and Scilla natalensis (status is Vulnerable in the Free State and KwaZulu-Natal).This association har bours the highest number of plant taxa with conservation status in the southern region of the SCPE and, together with plant community 2, the highest number of Red Data List taxa.
Environmental data: short rocky grassland communi ties on clay soils such as Mayo and Milkwood Forms, occurs on midslopes, scarps and crests of undulating norite hills on slopes of 3-9° on all aspects.Rock cover is 20-50% with rock size of 0.15-1 m in diameter (Table 3).
Diagnostic and dominant/prominent taxa: species group F contains the diagnostic species for this subasso ciation.with the taxa Helichrysum rugulosum, Pimpinella caffra and Tephrosia elongata (Table la).Other characteristic species include the forbs Acalypha puncta ta, Leonotis ocymifolia and Senecio lygodes, as well as the grasses Panicum natalense and Tristachya hiseriata.
Floristic diversity: a strong floristic affinity exists with all the subassociations of the association (Table la).The average number of species encountered per sample plot in this subassociation is 49, with the total number of plant species being a minimum of 130 taxa (14 relevés) (Table 3).Two plant taxa of conservation value are restricted to the subassociation (Table 2).

Digitaria eriantha Variant
Environmental data: rocky grassland on shallow clay soils of moderately sloped hill scarps and crests (Table 3).Rock size is 600 mm in diameter and cover is 25% (Table 3).
Floristic diversity: a strong floristic similarity exists with plant community 3.2.1,probably due to the similar ity in their rock size and cover (species group H; Table la & Table 3).Five SCPE endemics, five near-endemics and seven Red Data List taxa are found in this variant (Table 2).Of the 112 taxa recorded for the variant (seven relevés), only 15 are of conservation value (one is restricted to it).The average number of species encoun tered per sample plot is 47 (Table 3).

Alloteropsis semialata Variant
Environmental data: rocky grasslands on shallow clay soils occurring on relatively steep midslopes of hills.Rock cover is 35%, with rocks 350 mm in diameter (Table 3).
Floristic diversity: the community shares a floristic identity within various species groups (Table la).Five SCPE endemics, and seven near-endemics and seven Red Data List taxa are found in this variant (Table 2).It has 17 taxa of conservation value, the highest number for this paper, with only one taxon restricted to it.The aver age number of species recorded per sample plot is 51 (richest plant diversity of all the study area's grassland communities), with a total number of 130 plant taxa (seven relevés) (Table 3).
Diagnostic and dominant/prominent taxa: diagnostic species for this vegetation type is Berkheya seminivea and Drimiopsis atropurpurea.This subassociation is characterized by group G (Table la).Prominent taxa that occur in this vegetation unit are the forbs Acalypha punc tata, Argyrolobium transvaalense, Barleria ovata, Pachycarpus transvaalensis, Rhynchosia spectabilis, Tephrosia purpurea and Vernonia natalensis.Important grasses for this vegetation type are Brachiaria serrata, Diheteropogon amplectens, Setaria sphacelata and Themeda triandra.Prominent woody species include the geoxylic suffrutices Elephantorrhiza elephantina and Rhus discolor.
Floristic diversity: the community exhibits a strong floristic affinity with all the grasslands of the study area (Table la).The average number of species encountered per sample plot in this subassociation is 49. with the total number of plant species being a minimum of 119 taxa (nine relevés) (Table 3).No plant taxa of conservation value are restricted to it (Table 2).

Koeleria capensis Variant
Environmental data: relatively tall rocky mountain grassland on east-west aspects of steep midslopes and crests occurs on shallow clay soils, is covered by ± 30% rock, with a relatively large rock diameter (on average 650 mm) (Table 3).
Diagnostic and dominant/prominent taxa: no diag nostic species occur in this variant.Character species include the prominent forbs Crabbea hirsuta and Ipomoea obscura, and prominent grasses are Eulalia villosa and Koeleria capensis (species group G; Table la).Other dominant plants include the geoxylic suffrutex Rhus discolor and the small tree Euclea crispa.Grass cover is dense and species rich.
Floristic diversity: a strong floristic similarity is shared with plant community 3.1.1,probably due to sim ilarity in rock size and cover (species group H: Table la & Table 3).Of the 14 taxa of conservation value in this variant, five are SCPE endemics, six near-endemics and five Red Data List taxa (Table 2).The average number of species encountered per sample plot is 48.with a total of 119 plant species (6 relevés), the second richest plant diversity in the study area's grasslands (Table 3).

Berkheya seminivea Variant
Environmental data: rocky grassland communities on shallow clays of moderate midslopes and crests that are situated on east-west aspects (Table 3).Average rock size is 2(X) mm and cover is 40% (Table 3).
Diagnostic and dominant/prominent taxa: there are no diagnostic species, but characteristic species for this variant include the forbs Berkheya seminivea, Drimiopsis atropurpurea, Helichrysum cephaloideum and Thesium magalismontanum the most frequent (species group G: Table la).Other important taxa are Andropogon schirensis, Argyrolobium transvaalense, Eragrostis chloromelas and Rhynchosia spectabilis.Floristic diversity: this variant is floristically typical of its association, but is characterized by the absence of the sister variant's character species (species group H: Table la).Of its 13 taxa of conservation value, five are SCPE endemics, four near-endemics and six Red Data List taxa (Table 2).The average number of species encountered per sample plot is 50.with the total being 95 taxa (three relevés) (Table 3).
Environmental data: rocky grassland communities on black clay soils.The habitat is found on footslopes and mid slopes of undulating norite hills.The gentle slopes vary from 5-9°, with an east-west aspect the norm.Soils characteristic of these slopes is the Milkwood Form.Rock cover varies from 35-40% and rock size from 400-750 mm in diameter.
Diagnostic and dominant/prominent taxa: species group J contains the characteristic species for this subas sociation.with prominent forbs such Becium obovatum.Convolvulus sagittatus, Gerbera ambigua and Vernonia galpinii (Table la).The forbs Senecio microglossus and 5. latifolius, and the grasses Themeda triandra and Tristachya leucothrix are the most dominant in this sub association.Other important taxa are the woody species Elephantorrhiza elephantina and Euclea crispa.succu lents Aloe castanea and A. greatheadii.and grass species such as Eragrostis superba.Setaria sphacelata, Sorghum bicolor and Tristachya rehmannii.
Floristic diversity: a strong floristic affinity exists with certain plant communities of the association (species group J). but excludes plant communities 3.1.1and 3.4 (Table la).The average number of species encountered per sample plot in this subassociation is 46. the total number of plant species being 109 (six relevés) (Table 3).Although 15 taxa with conservation value occur in this subassociation (Table 2), namely five SCPE endemics, six near-endemics and six Red Data List taxa.no plant taxa with conservation value are restricted to it.
Environmental data: moist rocky mountain grassland on black turf soils lies on the lower part of gentle, sloped footslopes.3-5°.It is found predominantly on soils of the Arcadia Form.Rock cover is ± 15-30%, rocks, with a rel atively small average size of 100-250 mm in diameter (Table 3).
Diagnostic and dominant/prominent taxa: diagnostic species are represented by species group L ( Floristic diversity: the subassociation shows its strong floristic affinity within association 3 in species groups C and M (Table la).More detailed future studies could suggest its upgrading to the level of association.The average number of species encountered per sample plot in this subassociation is 44, with 77 plant species the total number (four relevés) (Table 3).Twelve taxa with conservation value occur in this subassociation (Table 2), namely four SCPE endemics, five SCPE near-endemics and five Red Data List taxa.No plant taxa with conser vation value are restricted to it.
Environmental data: this rocky mountain grassland occurs on deep black turf soils (500-750 mm) which lie on moderately sloped, lower footslopes and valley bot toms, 5-15°.It is found predominantly on vertic Arcadia and Steendal Forms.Rock cover is 10-40% and rocks have a small average size of 100-150 mm in diameter (Table 3).
Diagnostic and dominant/prominent taxa: diagnostic species are presented in species groups N (Table la) and are characterized by the small trees Rhamnus prinoides and Rhus rogersii, the grasses Brachiaria eruciformis and Setaria incrassata, and the forbs Indigofera evansiana, Kohautia caespitose and Striga elegans.Forbs are abundant in the vegetation unit and prominent species include Albuca setosa, Berkheya onopordifolia, Felicia muricata, Helichrysum albilanatum.H. nudifolium, Justicia anagalloides, Kalanchoe rotundifolia and Rubia horrida.Prominent grasses of the association are Alloteropsis semialata and Sporobolus pectinatus, and dominant grasses such as Brachiaria serrata, Eragrostis chloromelas, Heteropogon contortus and Panicum natalense.
Floristic diversity: the average number of species encountered per sample plot in this association is 44, with the total number of plant species being a minimum of 84 taxa (12 relevés) (Table 3).There are 11 plant taxa of conservation value in the association (Table 2), of which two are restricted to it, including Rhus rogersii, a shrub assessed as Insufficiently Known for Swaziland in the Red Data List.Environmental data: moist, cool mountain grassland on turf soils, lies on gentle, sloped footslopes, 3-5°, restricted to deep Steendal soils.Rock cover is ± 20-25% and rocks have an average diameter of 50-150 mm (Table 2).
Diagnostic and dominant/prominent taxa: diagnostic species are represented by species group O ( Floristic diversity", a floristic link with plant commu nity 4.2 in species group N, indicates the relationship between these two subassociations on turf (Table la), although the environmental data differ to a great extent.The average number of species encountered per sample plot is 46.The total number for this subassociation is 84 (four relevés) (Table 3).One plant taxon with conserva tion value, the near-endemic Rhus tumulicola var.meeuseana, is restricted to it.Nine taxa with conserva tion value occur in this subassociation and comprise four SCPE endemics, three near-endemics and two Red Data List taxa (Table 2).
Environmental data: wooded grassland communities on black turf soils.These units occur in valley bottoms between undulating norite hills.The gentle slope varies from 1-3° and eastern or western aspects are predomi nant.Soil characteristic of these slopes is the Arcadia Form.Rock cover is 5-10% and rock diameter is 50-100 mm (Table 3).
Diagnostic and dominant/prominent taxa: species group P contains the diagnostic species for this associa tion (Table la).Two trees are diagnostic for the associa tion, namely Acacia tortilis and Dichrostachys cinerea.Floristic diversityr.a floristic link exists with the more herbaceous plant community 4.1, in species group N (Table la), but a difference in vegetation structure is apparent.The average number of species encountered per sample plot is 41 (Table 3).The total number of plant species for this subassociation is 65 (four relevés).No plant taxa with conservation value are restricted to the community, although three SCPE endemics, three SCPE near-endemics and two Red Data List taxa were record ed.
Environmental data: wooded grassland associated with anomalous habitats (Siebert 1998) occurs on red clay and white loam soils of predominantly the Mispah Form that are characterized by serpentiniferous chemical compositions.It lies on moderate footslopes of 5-9° on all aspects of undulating hills.Rock cover is ± 20-70% and with large rocks 100-400 mm in diameter (Table 3).
Floristic diversity: the average number of species encountered per sample plot is 36.with the total number of plant species being a minimum of 72 taxa (nine relevés) (Table 3).Fifteen taxa of conservation value occur and the association (Table 2) has the highest num ber of taxa with conservation status restricted to it (seven), and includes plant species such as the near endemics Helichrysum uninervium and Lotononis wilm sii, and the endemic and Red Data-listed Jamesbrittenia macrantha.
Environmental data: wooded grassland of rocky foot slopes with clay soils.It lies on moderate slopes of 7-9° on north-south aspects of rocky ridges of magnetite.Soils are predominantly the Mispah Form.Rock cover is ± 60-70% and large rocks, 100-400 mm in diameter (Table 3).
Floristic diversity: the subassociation shows a floris tic affinity with the turf grasslands of the Roossenekal Subcentre in species groups V and W (Table la).A spe cific link with the grasslands of the study area, which includes its sister subassociation, is indicated in species group X.The average number of species encountered per sample plot is 39, with the total number for this subasso ciation being 70 (four relevés) (Table 3).Five SCPE endemics, six near-endemics and three Red Data List taxa are found in this subassociation (Table 2).Of its 11 taxa of conservation value, only the near-endemic Aneilema longirrhizum is restricted to it.
Environmental data: wooded, rocky grassland on white loam soils and is restricted to exposed norite sur faces.It lies on moderately sloped footslopes of 5-7° on all aspects.Soils are predominantly the Mispah Form.Rock cover is ± 20-70% and large rocks.100-200 mm in diameter (Table 3).
Floristic diversity: a slight floristic affinity is visible between this subassociation and plant communities 4.2 and 5.1 in species group V (Table la).The average num ber of species encountered per sample plot is 33, with the total number for this subassociation being 72 (five relevés) (Table 3).It is one of the syntaxa with the high est numbers of SCPE endemics and SCPE near endemics.It also has three Red Data List taxa (Table 2).Of its 14 taxa of conservation value, four taxa.namely the SCPE near-endemics Rhus keetii and Euclea linearis (form), and the SCPE endemics Ipomoea bathycolpos var.sinuatodentata and Poly gala sp.(Siebert 449).are restricted to it.This number is the second highest for any community in the Roossenekal Subcentre.
Environmental data: within the Roossenekal and Leolo Subcentres, this association represents hygrophilous vegetation of mountain streams and seepage areas and occurs on wet sites where rocks of ± 150 mm diameter cover ± 25% of the soil surface.These areas have gentle slopes (3°) and the soils are typically clay on solid rock, with a sandy alluvial layer on the surface.
Diagnostic and dominant/prominent taxa: species group AA (Table lb) contains the diagnostic species.Dense stands of the diagnostic sedge Schoenus nigricans and the diagnostic grass Hyparrhenia tamba dominate the vegetation.Other diagnostic forbs are Chironia purpurascens, Equisetum ramosissimum and Hypoxis argentea.Sedges such as Fuirena pubescens and Schoenoplectus corymbosus are also prominent, while Andropogon eucomis, Cymbopogon validus, Hyparr henia fdipendula and Imperata cylindrica are prominent grasses.Acacia karroo and Rhus leptodictya are the woody species that may occur in the association.
Floristic diversity: a strong floristic affinity with the wetland community 7 is indicated in species group AI and some relationships exist with the grasslands (species group Y) (Table lb).The azonal wetland vegetation is not as rich in plant diversity as the grasslands.The aver age number of species encountered per sample plot is only 27, with the total number of plant species being a minimum of 52 taxa (11 relevés) (Table 3).There are, however, four taxa of conservation value that occur in this association (Table 2), and two taxa with conserva tion status restricted to it.namely the Red Data listed orchid Disa rhodantha (Insufficiently Known), and the shrub, Nuxia gracilis (Insufficiently Known).
Environmental data: sparsely wooded, moist herbland and grassland along non-perennial mountain streams in rocky areas lying on gentle to moderate midslopes (5-7°).Rock size 350-750 mm in diameter and rock cover is 35-45%.
Diagnostic and dominant/prominent taxa: species group AB (Table lb) contains the diagnostic species for this subassociation, which include the woody species Acacia karroo, Nuxia gracilis and Rhus leptodictya.Diagnostic forbs are the fern Adiantum capillus-veneris, and the sedges Coleochloa setifera.Dittrichia graveolens and Juncus punctorius.Triraphis andropogonoides is a diagnostic grass.Prominent forbs are the sedges Fuirena pubescens, Schoenoplectus corymbosus and Schoenus nigricans.Andropogon eucomis, Aristida bipartita and Cymbopogon validus are the most dominant grasses.
Floristic diversity: a notable relationship exists with plant community 6.2 in species group AC (Table lb).
Environmental data: dense moist herbland (reedbed) and grassland along permanent mountain streams occurs on gentle midslopes and footslopes of 1-3°.Rock cover is ± 5-15% and small rocks, 50-150 mm in diameter (Table 3).Floristic diversity: a floristic affinity exists with the adjacent grassland plant community 3.4 (species group L) (Table la), and with the wetland plant community 7 (species group AG) (Table lb).The average number of species encountered per sample plot is 27, with the total number for this subassociation being 42 (three relevés) (Table 3).Only two taxa of conservation value, namely Red Data List taxa, are found in this subassociation (Table 2).
Environmental data: herbland and grassland occurs in moist valley bottoms or on mountain crests, usually in non-permanent seepage areas along streams.It is associ ated with gentle slopes of 1-3°.Scattered stones cover ± 10-20% of the soil surface with an average diameter of 50-100 mm (Table 3).
Diagnostic and dominant/prominent taxa: diagnostic species are presented in species group AD ( Floristic diversity: a strong floristic affinity exists with the grassland community 4.1 (species group O), but a distinct affinity also exists with the wetland plant com munity 7 in species group AH (Table lb).In this subas sociation the sedges are less prominent and should be seen as a moist grassland-wetland ecotone.The average number of species encountered per sample plot is 25, with 52 taxa the total number for this subassociation (four relevés) (Table 3).There are four taxa of conserva tion value that include one SCPE endemic, one SCPE near-endemic and three Red Data List taxa (Table 2).Environmental data: wooded herbland and grassland along larger rivers in valleys, such as the Steelpoort River.The vegetation covers the zone directly adjacent to streams, on permanently moist soils.The area has a gentle slope of 1-3°.Rock cover is ± 20-30% and rock diameter is 150-200 mm (Table 3).
Diagnostic and dominant/prominent taxa: diagnostic species are represented by species group AF (Table lb).The vegetation unit is dominated by diagnostic forbs, which include the prominent weedy aliens Conyza bonariensis and Flaveria bidentis, the sedges Cyperus marginatus, Mariscus rehmannianus, M. sumatrensis, and the forb Polygonum meisnerianum.The presence of weeds is the result of disturbance caused by annual floods.Salix mucronata is the diagnostic woody species and Eragrostis gummiflua the diagnostic grass.Hygrophilous grasses and sedges such as Miscanthus junceus and Schoenoplectus corymbosus are dominant.Acacia karroo and Rhus leptodictya are common small trees of the association.Andropogon eucomis, Cymbopogon validus.Hemarthria altissima, Hyparrhenia hirta and Imperata cylindrica are dominant grasses of the association.
Floristic diversity: a strong floristic affinity exists with the wetland plant community 6 (species group AI) and a weaker affinity with the grasslands (species group Y) (Table lb).The average number of species encoun tered per sample plot is 27, with the total number of plant species being 52 taxa (four relevés) (Table 3).This asso ciation has the lowest number of taxa with a conservation status (Table 2 Environmental data: this rare association represents dense herbland of moist seepage areas, recorded only on the summit plateaus of the Leolo Mountains around 1 800 m and is usually associated with black, marshy clay soils.A short, dense cover of nongrassy forbs dom inates the vegetation.It lies on gentle slopes of 1-3° and ± 10% of the soil surface is covered by small stones with an average diameter of 50 mm (Table 3).
Diagnostic and dominant/prominent taxa: diagnostic species are represented by species group AJ (Table lb).The most predominant diagnostic taxa of the association are the small forbs Limosella maior, Ranunculus meyeri and R. multifidus.Sporobolus centrifugus is the diagnos tic grass.Schoenoplectus corymbosus is a dominant sedge in the association.
Floristic diversity: a very slight floristic affinity exists with the other wetland plant communities of the area (species group AK) and also with the grasslands of the study area (species group Y) (Table lb).It is much relat ed to similar wetland communities below the Drakens berg escarpment above 1 800 m (Hilliard & Burtt 1987).The average number of species encountered per sample plot is 20. with the total number of plant species being 24 taxa (two relevés) (Table 3).Together with plant com munity 7, this association has the lowest number of taxa with a conservation status, namely two.These include the Red Data List species Eucomis autumnalis subsp.clavata.and the undescribed SCPE endemic Tulbaghia sp.(Siebert 1304), which may be a new genus of the Alliaceae.

Vegetation key
A dichotomous vegetation key is presented to facili tate identification of the various syntaxa found in the study area (Table 4).The definitions are broad indica tions of the syntaxa and should be seen as a guideline, rather than precise descriptions.A diagnostic characteris tic of the vegetation or habitat is given, followed by the most diagnostic and conspicuous species of a particular syntaxon.The first species listed is restricted to the spe cific syntaxon only, and the second is dominant in the syntaxon.but may occur in other syntaxa.Where one species is given, no species were restricted to the partic ular syntaxon only.

Ordination
A scatter diagram displaying the distribution of the relevés along the second and third ordination axes is presented for both grassland and wetlands in Figure 2 (eigen values: axis 2 = 0.471; axis 3 = 0.325) and Figure 3 (eigen values: axis 2 = 0.458; axis 3 = 0.256) respec tively.Vegetation units are represented as clusters, their distribution on the scatter diagram corresponding with certain physical environmental conditions.The gradient described by the x-axis in both instances, is related to drainage and hence, soil moisture.In the grasslands, the communties with the highest available soil moisture are situated at the left of the diagram (Figure 2), but com munities of the wetlands with poor drainage on water logged soils are to the right (Figure 3).In addition, com munities of the grasslands on clay soils of steep slopes are situated to the left of the diagram and communities on gravel soils of steep slopes to the right (Figure 2).The clay soils have the highest moisture availability, although the run-off is high.Grassland communities of turf soils on moderate slopes are positioned in the cen tre of the diagram, because these soils have a high soil moisture percentage, which is unavailable due to reten- tion by the soil particles.The gradient shown by the yaxis for communities of wetlands is that of topographic position (Figure 3).Here, the water systems of mountain slopes with a faster run-off are placed at the top of the scatter diagram.Perennial seepage systems of plateaus are centred in the middle of the diagram, and communi ties of permanent, slow-flowing rivers are located at the bottom.
The gradient along the first axis of Figure 2 is also an indication of the species diversity in the grasslands, with the species diversity at the left of the diagram being high er than that of the communities at the right.This phe nomenon can be attributed to the heterogeneous environ ment experienced by most Brachiario serratae-Melha nietum randii rocky grassland communities.
The gradients that have been identified are associat ed with each other and have a strong influence on the vegetation.The three most dominant and conspicuous taxa of each growth form (trees/shrubs/suffrutices, forbs/sedges and grasses) are given for each of the eight major vegetation types depicted in the scatter diagram (Table 5).

DISCUSSION
Plant diversity and geographic variations over south ern Africa are best explained by the geology (soils) and climate, with topographic diversity explaining much of the remaining variance (Holland 1978;Schulze & McGee 1978).Much of the distribution of the syntaxa in the study area can be attributed to fire, and the vegetation dynamics and historic evolution of the flora of the region (Siebert 1998), which is influenced by the above-men tioned three factors.
The TWINSPAN classification and its subsequent refinement by Braun-Blanquet procedures resulted in the delineation of 17 syntaxa.These plant communities can be related to certain environmental factors, the gradients of which are illustrated in the DECORANA scatter dia grams.The major gradient relates to soil moisture, which in turn is a direct consequence of run-off and drainage in the case of grasslands, permanent water bodies/sources in the case of wetlands, and temperature (drought stress) in both cases.Soil moisture availability is determined by the soil type, which in turn was determined by the topo graphical position of the substrate during pedogenesis.The gradients of the diagram are therefore a direct con sequence of topography and climate.
In the SCPE.soils of ultramafic origin have caused the development of syntaxa adapted to the specific soil conditions, with high concentrations of certain elements, notably heavy metals.Such a plant community (syntaxon)-soil association on ultramafic substrates has previ ously been identified for southern Africa, on the Great Dyke of Zimbabwe (Werger et al. 1978) and the Barberton Greenstone Belt in South Africa (Morrey et al. 1989).Because of the ultramafic nature of the norites of the Roossenekal and Leolo Subcentres, many taxa of the study area are uncommon or absent in other grassland areas of southern Africa.
Among the 17 plant communities.44 plant species/ infraspecific taxa were identified as of conservation sig nificance.Fifteen were SCPE endemics and 19 SCPE near-endemics.Of the 44, 17 were listed in the southern African Red Data List for plants (Hilton-Taylor 1996).This number compares well with serpentine sites else where in the world, namely 18 rare plants and endemics in central Queensland.Australia (Batianoff et al. 1995), 20 endemics on the Great Dyke.Zimbabwe (Wild 1965) and 22 endemics in southern Mpumalanga.South Africa (Balkwill et al. 1995).
Species richness of Sekhukhuneland grassland com munities is high when compared with the grassland species richness of other parts of South Africa.Sekhukhuneland grasslands have a species richness of 20 to 51 species per 100 n r with a mean of 38 species (Table 3).This mean is higher than that recorded for the grasslands of the northeastern Drakensberg (Mpuma langa) and southern Drakensberg (Eastern Cape), but is lower than that of the Highveld (Gauteng/Mpumalanga) (Hoare & Bredenkamp 2001).Floristically the Grass lands of the study area are related to those described by Bloem (1988).Deall et al. (1989), Matthews et al. (1992a).Burgoyne (1995) andSmit et al. (1997).
Throughout the SCPE. the remaining natural popula tions of plants and animals are under intense pressure from exploitative land uses.There are certain areas with specific syntaxa that should be considered as a priority for conservation purposes.Some plant endemics of the southern region of the SCPE are restricted to specific syntaxa and these habitats therefore require urgent atten tion for conservation as a result of the rapid expanding mining industry, a common threat to southern Africa's rich plant diversity (Dold & Johnson 1997).Biodiversity increases ecosystem stability by promoting diversity among species in their responses to environmental fluc tuations (Naeem & Li 1997;Grime 1998;Ives et al. 1999) and hence, is imperative for successful conserva tion initiatives.The establishment of nature reserves or protected areas is one solution to this problem of biodi versity loss; this is best achieved through land use strati fication derived from a holistic overview.Such a strate gic environmental assessment, which includes an ade quate database of natural features and other land uses (Bedward et al. 1992), should be a priority for conserva tion agencies in the region.
The priority vegetation types for conservation (hotspots) are associations 2, 3 and 4, of which subasso ciation 3.1, the Brachiario serratae-Melhanietum randii helichrysetosum rugulosi rocky grassland on the scarps and crests of norite hills, is probably the most important and threatened.It should also be noted that the wetlands are sensitive systems that are easily disturbed and should be protected (Doust & Doust 1995;Van Wyk et al. 2000).Important wetlands to conserve are the seepage areas, namely the Limosello maioris-Ranunculetum meyeri Association and the Fuireno pubescentis-Schoenetum nigricantis bulbostylietosum hispidulae Subassociation.
Alien species primarily invade areas of high indige nous species richness (Lonsdale 1999;Stohlgren et al. 1999), such as the grasslands of southern Africa.Acacia dealbata, an alien tree from Australia, has invaded large areas of the Roossenekal Subcentre and especially the adjacent Steenkampsberg.Removing these trees is total ly dependent on the owner of the land, with no largescale projects being implemented.It is an ironic situa tion, with people 50 km to the north extensively chop ping down indigenous bushveld trees for firewood.This description and classification of the syntaxa of the study area is a contribution towards the understand ing of the vegetation and flora in the southern parts of the SCPE and the region as a whole.The information sup plied here should be applied in the management and con servation of the vegetation and habitats, especially the rocky grasslands that are threatened by the mining indus try and inappropriate forms of land use, specifically overgrazing by domestic stock.This paper provides a basis for proper and sound assessment of the region's vegetation, as it includes aspects such as species rich ness, rarity and habitat preference.Detailed site-specific studies, using this paper as a reference, remain a prereq uisite before suggestions concerning mining or conserva tion can be made.The region boasts a rich natural and human history (Pollock et al. 1963), and representative ecologically viable portions of the grasslands of the region, as well as the wetlands, should be protected and conserved for future generations.

FIGURE 1 .
FIGURE 1.-Location of the grass lands of the study area in the Northern Province and Mpu malanga, South Africa.

FIGURE 3 .
FIGURE 3.-Relative positions of all the releves along the second and third axis of the ordination of the wetland vegetation of the Sekhukhuneland Centre of Plant Endemism.Numbers correspond with those of syntaxa inTable lb and in the text.

îilliiiiiliiiililn lllfiil Species group shared with Table Ib Species group Y
Table la).Euryops brevipapposus, Helichrysum splendidum and Vemonia myriantha are the most promi nent diagnostic species of this syntaxon.Other diagnos tic species include the shrub Buddleja saligna and the herbaceous Lotononis foliosa and Xerophyta viscosa.There are no diagnostic grasses, but dominant species include Eragrostis capensis, E. curvula and Tristachya leucothrix.A prominent forb is Pentanisia prunelloides, while the shrub Protea caffra (endemic form) is conspic uously present.

Not threatened in northern provinces o f South Afnca. but in other areas o f southern Africa. Abundance in communities: 1. abundant: +. frequent; r, rare;. absent. Collectors: P = P.S. Swartz; S = S J . Siebert; W = A.E. van Wyk. Blocks represent community/syntaxon specific taxa.
da and Olinia emarginata.Diagnostic forbs are Thesium burkei, the succulents Crassula sarcocaulis and Aloe pretoriensis, and the geophytes Boophone disticha and Zantedeschia pentlandii.Aristida junciformis and Cymbopogon excavatus are the diagnostic grasses of this association.Prominent plants are the succulent Aloe castanea, the shrubby Rhoicissisus tridentata and the grass es Eragrostis pseudosclerantha, Themeda triandra and Tristachya leucothrix.
Table la).The dominant diagnostic forbs are Callilepis leptophylla, Dicoma zeyheri, Gnidia cap it at a, Melhania randii and Vemonia oligocephala.Woody species typical of the association include the geoxylic
/prominent taxa: character istic species are represented by species group AC and AG (Table lb).No woody or grass species are diagnostic of this community.Characteristic forb species include the sedges Cyperus sexangularis and Kyllinga erecta, and the forb Berula erecta.Dominant grass species are Miscanthus junceus and Phragmites australis, the forbs Pycnostachys reticulata and Senecio gerrardii, and the sedges Fuirena pubescens, Schoenoplectus corymbosus and Schoenus nigricans.Andropogon eucomis, Cymbo pogon validus and Hyparrhenia fdipendula are promi nent grasses.
), including the Red Data List taxon Eucomis autumnalis subsp.clavata.which is classified as Rare in the Free State and Vulnerable in KwaZulu-Natal, and the SCPE endemic form of Acacia karroo.