Patterns of plant diversity and endemism in Namibia

Species richness, endemism and areas that are rich in both species and endemic species were assessed and mapped for Namibia. High species diversity corresponds with zones where species overlap. These are particularly obvious where there are altitudinal variations and in high-lying areas. The endemic flora o f Namibia is rich and diverse. An estimated 16% of the total plant species in Namibia are endemic to the country. Endemics are in a wide variety o f families and sixteen genera are endemic. Factors that increase the likelihood o f endemism are mountains, hot deserts, diversity o f substrates and microclimates. The distribution o f plants endemic to Namibia was arranged in three different ways. Firstly, based on a grid count with the phytogeographic value o f the species being equal, overall endemism was mapped. Secondly, range restricted plant species were mapped individually and those with congruent distribution patterns were combined. Thirdly, localities that are important for very range-restricted species were identified. The resulting maps o f endemism and diversity were compared and found to correspond in many localities. When overall endemism is compared with overall diversity, rich localities may consist o f endemic species with wide ranges. The other methods identify important localities with their own distinctive complement o f species.


INTRODUCTION
Species diversity was traditionally measured by count ing the number of different species recorded in a specific area or grid (Linder 2001).The 'weight' of the species was not taken into consideration.Today various measures of diversity have been proposed that give greater value to species that are taxonomically, geographically, ecologi cally or economically distinct, but no "best' method for mapping species diversity has yet been found (Craven 2002b).The development of floristic databanks allows quick and efficient retrieval of phvtogeographic data that can produce computerized distribution maps.This study used the computerized data of specimens housed in the National Herbarium of Namibia (WIND) and the National Herbarium in Pretoria (PRE) to survey distribu tion patterns of plant diversity, overall endemism and centres of endemism and diversity on a quarter-degree scale in Namibia.The endemic flora were also analysed and factors that may have contributed to the resulting distribution patterns were discussed briefly when evi dent from the use of map overlays.Known centres of endemism were not redefined, only species with similar patterns of distribution were recorded.Caldecott et al. (1996) separated the current knowl edge of biodiversity into global, regional, national, ecoregional and site information.Patterns of diversity in Namibia have been shown on continental-scale diversity maps (Mutke et al. 2001) and included in region-based studies such as those of Goldblatt (1978), Cowling et al. (1989) and Gibbs Russell (1985, 1987).The account of Linder (2001) on patterns of plant species endemism and richness for the African flora does not include arid areas such as most of Namibia, The first national assessment and map of relative species richness in Namibia was that of Maggs et al. (1994).It was based on distributional data per magiste rial district following Merxmiiller (1966Merxmiiller ( -1972)), as well as other literature.Species diversity was re-assessed for the Biodiversity Country and mapped on half-degree grid squares (Maggs 1998;Maggs et al. 1998).This study updates the underlying data used in Maggs (1998) on a finer scale.
A taxon is endemic if confined to a particular area (Major 1988) which may be large or small.Clearly, data on endemism would be more useful if given by floristic province rather than political divisions (Major 1988;Van Wyk & Smith 2001), but datasets between different countries are seldom compatible in quality' or quantity.Due to the fact that Namibia is home to a considerable number of endemics with adequate data, this assessment only reviews species limited to Namibia (Figure 1).An endemic is therefore defined here as a taxon that is restricted to within the political borders of Namibia.Taxa that extend marginally into another region, i.e. beyond the political borders of Namibia are referred to as near endemic.
Centres of outstanding species diversity and endemism such as the Kaokoveld and Gariep have long attracted attention, but their boundaries, floristic elements and origins remain fairly sketchy.Different approaches and methodologies have also contributed to the centres (sometimes with the same name) not being compatible or comparable (Van Wyk & Smith 2001: Craven 2002b).Stott (1981) suggested that the process consists of stages i.e. after taxonomic study (essential for elucidating closely related taxonomic units) using specimens, spe cies distributions are plotted and areas of congruence identified.The plants are then arranged into recognizable groups, which on further analysis would identify phyto geographic centres determined by a high concentration of taxa with restricted distributions.This approach was pioneered in southern Africa by Weimarck (1941) and is found in taxonomic literature, for example in Nordenstam (1969) and Hilliard (1994).The approach looks at the geographical ranges of species regardless of their growth form or other factors such as topography and present climate, and identifies particular geographical areas inhabited by species that are restricted to these ranges.
Once such a centre is recognized, explanations are sought on how they may have arisen (e.g.past climate) and how they are being maintained.This knowledge is fundamen tal to understanding the origin, migration, and speciation of plants and is essential for developing strategies for biological conservation.This study did not attempt to redefine the centres presently known for Namibia, but attributes a number of new species to the centres.
Maps presenting overall patterns of diversity and endemism in Namibia have been used to identify regions of importance for conservation (Simmons et al. 1998;Mendelsohn et al. 2002).This paper shows two other methods of mapping important areas for endemics, which should also be taken into consideration.

Database
Georeferenced specimens on the specimen database (SPMNDB) in WIND provided the grid-diversity count.This database has ± 120 000 specimens and includes specimens housed in PRE that were collected in Namibia.All specimens of higher plants were used in the evalua tion.A sizable proportion was georeferenced following the quarter-degree square system of Edwards & Leistner (1971).Gaps in coverage due to collecting biases and database input errors were corrected where possible (Craven 2002b).The number of species present in each quarter-degree square was calculated and mapped.
Distribution data for endemic species were obtained from the specimen dataset as well as literature sources.Records for endemic species were found in 722 out of over 1 200 quarter-degree squares in Namibia.These were variously arranged and mapped: 1, endemic fami lies, genera and species individually; 2, the number of endemic species per quarter-degree square; 3, the number of quarter-degree squares in which species occurred; and 4, areas where species restricted to only one or two quar ter-degree squares were found.

Degree scale
Quarter-degree squares were chosen for the grid scale in order to show patterns of distribution on as fine a resolution as possible and allowing small or more localized centres of diversity to be apparent.Sufficient information at that scale is available for Namibia and the total area or number of quarter-degree square grids is manageable.Where no or few records were recorded in a quarter-degree square, the grids were 'revisited' and any such 'empty' square individually rechecked and improved.Records from keyword searches and literature sources, i.e. checklists for specific areas such as those of Rodin (1985), Giess & Snyman (1986), Hines (1992) and Clarke (1999) as well as collections of the first author, were incorporated.

GIS data
Shapefiles produced in ArcView [Environmental Sys tems Research Institute (ESR1) 2000] of Namibian fea tures such as soils, topography and rainfall by the Agro-Ecological Zoning Programme ( 1996-ongoing) and Atlas of Namibia Project (2002), as well as the positions of important mountains (adapted from Irish 2002) were superimposed onto the grid-based plant data.They were used to draw accurate borders, define localities and help pinpoint possible reasons for the variations in diversity.Profiles showing altitude change across the country that were taken at selected latitudes to cut through various notable topographic features (Atlas of Namibia Project 2002) were also overlaid.The vertical scales have been exaggerated to highlight the changes in altitude.
The methodology and tables used, and examples of all stages of the process, is described in more detail in Craven (2002b).

Inventory
The inventory of species endemic to Namibia, taxo nomic limits and nomenclature of species follows Craven (1999).The numerous sources for endemic status and updates are listed in Craven (2002b).Genera listed as endemic follow Leistner (2000).Over 600 species (Appendix 1) were investigated and eventually, records for ± 540 endemic spermatophyte species were avail able for the analysis and maps.Not all endemics were included in the analysis because endemism in some genera appears inflated due to numerous infraspecific taxa (Maggs et al. 1998), whereas other genera e.g.Crassula (Crassulaceae), Euphorbia (Euphorbiaceae), Salsola (Chenopodiaceae), Tetragonia (Aizoaceae) and some in the family Mesembryanthemaceae need to be revised.Species that are known to occur just over the border of the country were not included, e.g. a number of species in the genus Commiphora (Burseraceae) and family Acanthaceae, particularly the genus Petalidium.

Maps
Arcview (ESRI 2000) was used to produce the maps.Overall species richness and overall endemism could therefore be superimposed to find possible geographical correlation.Similarly, the shapefiles of the ± 540 species endemic to Namibia for Craven (2002b) were overlaid and the resulting maps scrutinized for congruent patterns.Areas were identified and their species listed, because as Bothalia 36,2 (2006) Van Wyk & Smith (2001) point out, such areas will have their own distinctive complement of species.
Endemic species not included by previous authors were assigned to known centres, i.e.Kaokoveld.Gariep, Waterberg-Otavi and Namibia Central and Southern Highland Centres, where possible.This required looking at locality data of collected specimens for the last two centres, as elements occur at higher elevations or on a specific substrate.The large data set of georeferenced specimens was also used to find subcentres or more localized areas of significance.

Overall patterns o f species richness and endemism
Species diversity is higher in localities where one veg etation type shifts to another.Variations in altitude and the maximum altitude in any grid are also significantly related to grid diversity (Figure 2).Only two localities in the northeast region can attribute high species richness to high rainfall.Where summer rainfall species overlap with winter rainfall species, however, there is an increase in diversity, e.g. the Rosh Pinah area.Another influenc ing factor is mist that occurs along the Namibian coast, which may be responsible for more favourable micro climates and increased species richness inland, e.g. the Namukluft near Rosh Pinah and Aus areas.
Namibian endemics were not found in the northeast, which forms part of the Zambezian Domain of Wrhite (1983) as this domain continues into countries further north.The southeast is part of the Kalahari Desert, which extends into Botswana, and no endemics were found there because of the general paucity of species and the artificial definition of endemic used here.In the rest of Namibia, the map of overall distribution of endemic species does not show any particular spatial pattern.
Localities where the quarter-degree squares with the most endemics occur, are often associated with mountains in Namibia.The best example is the Brandberg, which also confirms that endemism increases when mountains are located in deserts.Substrate-specific endemic plants are well known and in Namibia, four Jamesbrittenia species occur only in the limestone of the Waterberg-Otavi area (Hilliard 1994).Hot deserts have very high endemism in spite of their limited flora and vegetation and this has been shown in Namibia by the number of endemic spe cies confined to the Namib (Craven 2002b).ArcView shapefiles for physical features of Namibia, e.g.soils, aspects of climate, did not show marked patterns of simi larity at this level of resolution.
Geographical comparison of the overall pattern of diversity and that of endemism, as well as areas of importance for localized endemics and that of overall endemics, show a degree of congruence.Important local ized areas however, do not always coincide.Because the count is based purely on the number of species or endemics within that square, areas of richness cannot be distinguished by a particular combination of plant spe cies or endemics.In addition, squares with associated floral elements cannot be identified.Thus a particularly rich area may consist of very widespread species.

Families endemic to Namibia
There are no families of higher plants restricted to the political borders of Namibia.The most well-known fam ily that occurs only in southwest Angola and Namibia is Welwitschiaceae.

Genera endemic to Namibia
The natural ranges of sixteen genera fall with in Namibia (Figure 3).They are listed in Table 1 with an indication of the number of quarter-degree square grids in which they have been found.With the exception of the genus Ondetia (Asteraceae), most of the endemic genera occur in the central and west ern parts of Namibia.Arthraerua (Amaranthaceae), Marlothiella (Apiaceae), Eremothamnus (Asteraceae), Namibia, Synaptophyllum (Mesembryanthemaceae) and Neoluederitzia (Zygophyllaceae) occur along the coast, whereas Baynesia (Apocynaceae) and Namacodon (Campanulaceae) grow at higher altitudes.Manuleopsis (Scrophulariaceae) is fairly widespread, but generally found on higher ground.Chamaegigas (Scrophulariaceae) is a hydrophyte that inhabits pools in granite outcrops in central Namibia.
All four genera in family Mesembryanthemaceae occur in the winter rainfall region of southwest Namibia.Family Apiaceae, with two endemic genera, is of par ticular interest as it has very few representatives in spe cies and number of individuals in Namibia.A recently described genus, Baynesia (Bruvns 2000), attests to the fact that new genera may still be described in Namibia, especially in certain families that require revi sion, e.g.Mesembryanthemaceae. Ondetia occurs close to Botswana and may eventually be found there (Craven & Klaassen 1998).It is very closely related to Geigeria (which is presently under revision) and often mistaken for a Geigeria species in the field.

Species endemic to Namibia
Approximately 600 of the nearly 4 000 indigenous species recorded for Namibia are considered endemic to within the borders of the country (Figure 4) and are found in many different families and genera; 62 of the 157 families in Namibia have endemic species, whereas 231 genera out of 958 genera have endemic species.The most important families are the Mesembryan themaceae.Asteraceae and Acanthaceae.The genera Aloe (Asphodelaceae), Euphorbia (Euphorbiaceae).Hermannia (Sterculiaceae), Jamesbrittenia (Scrophulariaceae), Petalidium (Acanthaceae), Salsola (Crassulaceae), Stipagrostis, Eragrostis (Poaceae) and Zygophyllum (Zygophyllaceae) have the most endemic species besides Conophytum and Lithops (Mesembryanthemaceae), which have numerous infraspecific taxa.Distributions of about 600 endemic species and certain families and genera are mapped in Craven (2002b).Two examples showing distinctive patterns are illustrated here.Family Mesembryanthemaceae (Figure 5) is mainly restricted to the southwestern comer of Namibia which is also the only area with winter rainfall.Figure 6 shows endemism in Commiphora which occurs more commonly in the north with few plants in the winter rainfall zone.Some species have very widespread distributions and are well represented in the collection, whereas others are limited to one locality and one collection.One endemic was recorded in 195 different quarter-degree squares, and nine quarter-degree squares had more than 40 endemics.The quarter-degree square with the highest number of species were tabulated (Table 2) and the grid in which the Brandberg occurs is shown to have the most endemic species, followed by the Windhoek area.
Species endemic to localized areas are found mainly in western Namibia, but also in the central regions associated with high elevations.A number of localities were found to house four or more very restncted-range species.
The dominant life form of the endemics of the south west winter rainfall region is succulents, whereas further inland, i.e. east of the Hunsberg.dwarf shrubs are more common.The only region with endemic trees is the Kaokoveld.The distribution of endemic grasses shows them to be widespread.

Namibian near-endemic species
Near-endemics are defined here as species that extend marginally into another region, i.e. beyond the political borders of Namibia.Two noteworthy areas for endem ics and near-endemics in Namibia have been identified under the auspices of the IUCN Plant Conservation Programme.These centres of exceptional species rich ness and endemism (Davis & Heywood 1994) are the Kaokoveld in the northwest and the Gariep in the southwest.Further analysis of near-endemics is needed, including the species in this study.The number of species per quarter-degree square in the northwest and south will be higher.

Kaokoveld Centre
Considering the topography and climate, it is no wonder that mapped plant distributions show two main subregions besides the Brandberg, namely the coastal strip, which is affected by fog and cooler temperatures, and the inland highlands.Endemics of the coast in clude Ectadium rotundifolium, Merremia multisect a, Hermannia gariepina and grasses such as Chloris flabellata and Sporobolus virginicus.Most of the endemic taxa occurring on the highlands will not be found on the coastal plains.They are more numerous and often con fined to mountainous areas.
Subcentres of importance are the Baynes Mountains and the area around Sanitatis and Orupembe.Both areas have six localized endemics each.Four endemics are found in the Sesfontein area.The family with the most endemics is the Acanthaceae with five representatives and the other endemics are from a w ide variety of fami lies.

Gariep Centre
Relatively numerous local endemics were found around Aus, the Huib Hoch Plateau to Namus Mountains, the Hunsberg and a section of the Warmbad District.Species limited to these subcentres come from a variety of families and vary from grasses and geophytes to suc culent Euphorbiaceae and Mesembryanthemaceae. Life form type shows a certain degree of uniformity in some of the subcentres.Dwarf shrubs such as Caesalpinia merxmuellerana and Petalidium cymbiforme are charac teristic of the endemics of the Hunsberg, whereas more succulent species, including three in Euphorbia, are found on the western side of the Hunsberg in the Numas Mountains.Three succulent mesembs are also endemic to the Warmbad District, namely Antimima eendornensis, Schwantesia constanceae and S. succumbens.No spe cific life forms are characteristic of the Aus area, which is characterized by varying substrates, or the Huib Hoch Plateau areas.Although field work will probably result in many of these species being recorded further afield, some conspicuous plants such as Caesalpinia merxmuel lerana and Zygophyllum giessii have not been found to be widespread despite intense searching.

Waterberg-Otavi Centre
Additional species restricted to this centre identified here, but not necessarily only occurring on limestone, are Heteromorpha papillosa (Apiaceae), Pentatrichia avasmontana (Asteraceae).Plectranthus dinteri (Laniiaceae) which is also in the Windhoek region, and Thesium xerophyticum (Santalaceae) also on the Gamsberg.In addition, Thesium is in need of revision and although both the genera Plectranthus and Heteromorpha have been revised, little or no field work was carried out in Namibia.Pentatrichia is presently under revision.Species reported to date only from the Waterberg are Dintera pterocaulis (Scrophulariaceae), Eriospermum citrinum and E. lavranosii (Eriospermaceae).
Central Namibia and Southern Highland Centre Fifteen Manuleae (Scrophulariaceae) were found to occur in a highland centre (Hilliard 1994) that includ ed the Brandberg, Erongo, Khomashochland.Auas, Gamsberg.Naukluft.Tiras, and surround ing high ground, usually above ± 900 m.It excludes the limestone area of the Waterberg.but may stretch into Botswana.An analysis of mapped endemics and habitat data show that numerous range-restricted spe cies are confined to higher elevations, as prescribed by the definition of this centre by Hilliard (1994).The flo ristic elements range from shrubs (Nicotiana africcma) and dwarf shrubs (Corchorus merxmuelleri, Hermannia merxmuelleri) to geophytes (Haemanthus uvasmontanus, Lapeirousia avamontana) with a tew very localized suc culents (Ehracleola montis-moltkei.Euphorbia monteiroi subsp.brandbergensis, Aloe viridiflora).

DISCUSSION
Numerous hypotheses have been proposed to explain patterns of species diversity (Schmida & W ilson 1985), but none have been found to apply well to all bodies of data.Underlying datasets and resolution can also result in different patterns of diversity.This is seen when Namibia is mapped continentally (Mutke et al. 2001), regionally (Rebelo 1994) or nationally (Maggs et al. 1994).In spite of the finer resolution used here, the most species-rich areas in Namibia do not differ much from those first indicated (Maggs et al. 1994).The differ ences lie in better definition of the boundaries, additional localities and important smaller localities.Examples are the Naukluft.Windhoek and Aus regions.The inclusion of the Naukluft as an important area by Maggs et al. (1994) was suspected to be an artifact of high collecting intensity and this was proved here to be the case.On the other hand, species richness in the Windhoek area is not necessarily an artifact of good collecting, despite being close to a high population of potential collectors.It includes the second highest mountain in Namibia (Irish 2002), and a number of grasses (Klaassen & Craven 2003), and other species that are not known from else where in Namibia are found here.It indicates that this flora includes outliers from more distant areas and is in agreement with Major (1988).who considers mountains to be mesic refugial islands, which form ideal refuges in times of climate change.Another area of high diversity, near Aus, housed a concentration camp during World War II where the interned German citizens botanized to pass the time.Factors that contribute to the richness of this area include the diverse nature of the topography (the start of the escarpment) and varying substrate (scattered granite outcrops in the area) as well as the fog coming inland from the coast.
Although the plant species diversity map is the most detailed map of its kind for Namibia, care should be taken before using it for management purposes or predic tions.Both the delimited areas and the numbers of spe cies predicted for the regions need further refinements.Two aspects of conservation value that it does indicate are: 1, that many areas are more diverse than may appear during periods of harsh conditions, which may last for years or decades; and 2, the relationship between areas set aside as formal conservation areas and diversity.It is apparent that certain areas of high species richness are not afforded any formal protection.
The first map to show the overall distribution of endemic species in Namibia (Maggs et al. 1994) was based on 145 species.Endemics of southern Africa, including Namibia, were mapped by Rebelo (1994).Differences between the latter map (regional) and the present one for Namibia (national) are noticeable because of the scale, definition of the word endemic, and datasets used.Maps published in Simmons (1998) and Simmons et al. (1998) were based on updated data in Maggs et al. (1997) using half-degree squares, because accord ing to Simmons et al. (1998), bird data show that this scale reduces collecting bias.The results presented here justify the use of quarter-degree, because working on a national level, more quality control of the data is pos sible and other sources such as literature, field work and shapefiles of physical features can be used.An undefined 'escarpment' area was said to be the main centre for endemic plants by Simmons et al. (1998).Overlaying a defined escarpment developed by the Atlas of Namibia Project (2002) onto the endemic data indicates that this is only partially correct.Although there is an association between increased numbers of endemic species and the escarpment, the area between the northern and southern escarpments also show localities of importance, not only in general, but also for those with limited ranges.
The maps resulting from this study are published by the Atlas of Namibia Project (2002), where they are also combined with maps of Namibian fauna.Mendelsohn et al. (2002) conclude that the most notable zones of high diversity for fauna and flora occur in the northeast, in the Karstveld around Tsumeb. in highland areas in the centre of Namibia, and in various scattered areas of higher ground further west.Plant endemism was also combined with that of animals, and Mendelsohn et al. (2002) conclude that the overall patterns of endemism in Namibia are quite different from those of overall diver sity.The greatest majority of endemics are found in the dry, western and northwestern regions of Namibia.On a regional scale of plants only (and lower resolution), Rebelo (1994) reports a stronger correlation between species richness and endemicity.
Namibian endemic plants, as in other parts of the world, are usually associated with altitude, substrate, or variations in geography, which provide numerous microhabitats.The most important areas for species richness in Namibia, however, are 'transitional' areas, which Shmida & Wilson (1985) define as areas between different ecological regions, i.e. zones in which species overlap.Variations in altitude and the maximum altitude in any grid are significant as reported for Africa as a whole (Linder 1999).Superimposing altitudinal profiles onto the shapefile of species richness shows this clearly (Figure 2).It is also substantiated by studies which show variations in species diversity with altitude for specific sites or localities (Moisei 1982: Rutherford 1992).
Centres of diversity and endemism in Namibia, such as the Kaokoveld and the Gariep Centre, although lacking consistency in definition, have been discussed by numer ous authors.Volk (1964) proposed a Kaoko Element, which was elaborated on by Nordenstam (1974).Hilliard (1994) included two taxa, Jamesbrittenia eanescens var.laevior and J. heucherifolia (Scrophulariaceae), which are confined to southern Angola and northern Namibia.Other authors that recognized the Kaokoveld Centre are Hilton-Taylor (1994a), Maggs et al. (1994), Maggs et al. (1998), Van Wyk & Smith (2001) and Craven (2002a).Hilton Taylor (1994b) considers the Gariep to be essen tially a geographic rather than a phytogeographic centre, but both Nordenstam (1969) and Hilliard (1994) recog nize it as a taxon phytogeographic centre of importance for numerous species.
Mapping all Namibian endemics has shown that the distributions of many elements need to be reas sessed.Species presently regarded as e.g.Kaokoveld elements, ( Welwitschia mirabilis, Acanthosicyos horridus, Cyphostemma currorii, Acacia robymiana and Moringa ovalifolia) may stretch far beyond what is generally regarded as the centre.Another example is the Brandberg, which is considered an outlier of the Kaokoveld Centre by Nordenstam (1974) andHilton Taylor (1994a).Provisional results of the floristic ele ments of the Brandberg (Craven & Craven 2000) show that numerous range-restricted species also occur on other highlands further south and it is rather a part of the Highland Centre as suggested by Hilliard (1994).
The Kaokoveld and the Gariep Centres are basically geographic regions, so inclusion of species within the centres was based on presence or absence in the area.This is not possible with the Namibia Central and Southern Highland Centre and the Waterberg-Otavi Centre as they are identified by determinants such as habitat or substrate specificity.These centres do not show a clear geographic pattern of distribution on a map until altitude contours or outlines of mountains are included.More endemic spe cies will probably be included in these centres once more is known about such habitat requirements.
The name, Gariep, has also been used in large-scale mapping by Jurgens (1991) despite a different approach, i.e. including life form and climate in the analyses.Such approaches must not be confused with that of taxon phy togeography as discussed here.
In general, the variable nature of most aspects of Namibia's rainfall, as well as the paucity of overall cli matic data, precludes using climate at this level of resolu tion.It is, however, true to say that Namibia differs from Africa as a whole, because the most species-rich areas are in the wetter parts of the continent (Linder 1999).This study highlighted the need for the microclimatic conditions in which so many endemics thrive, to be stud ied and documented in a systematic way.Defining these habitats is essential to understanding the distributions of endemic plants.The same can be said for peculiar or iso lated substrata (serpentine, limestone, quartzite, calcare ous sands) which is a widespread phenomenon in some areas (Major 1988;Cowling et al. 1992), and Namibia is no exception.
Although distribution of endemics among life form classes was not studied here in detail, it is evident that life forms change with locality as recorded for endemic species in general (Major 1988).This is ascribed to climate, history of the flora and competition with the associated flora (Major 1988).
Certain taxa require floristic study and field work, but a provisional assessment suggests that a locality may be home to a variety of species from various taxonomic groups as suggested by Cowling et al. (1992).
Knowledge of local endemism will help create a bet ter basis for future policy (Brenan 1978).This study does provide sufficient information on certain aspects of Namibia's endemic plants to start formulating conserva tion strategies, but there is still a need for satisfactory taxonomic knowledge as well as more distribution data.It is also imperative that the information is used correctly.Simmons et al. (1998) concluded that another 11% of the land area would be required to protect Namibia's endemic plants.If the endemic plants already found within protected areas had been removed from the data set prior to the analysis, the resulting value would be much lower.No matter how highly a species is regarded, as soon as it is adequately conserved, it is no longer used as an argument to conserve another area (Kirkpatrick 1983).Because species are not spread evenly around the world and unique concentrations may occur in relatively small areas, i.e. within the political borders of a country' like Namibia, the onus is on Namibia to protect these species.

FIGURE
FIGURE 1.-Namibia, its neigh bours, capital city and some important mountains and towns.

FIGURE
FIGURE 2.-G nd-di\ersity for Na mibia depicted in five classes with altitude profiles showing correlation between changes in altitude and diversity.

FIGURE 3 .
FIGURE 3.-Distribution and num ber o f Namibian endemic gen era per quarter-degree grid.

FIGURE
FIGURE 4.-Distribution and num ber o f Namibian endemic spe cies per quarter-degree grid.

FIGURE
FIGURE 5.-Distribution o f endem ic plants in Mesembryanthe maceae and diversity per quar ter-degree grid.

FIGURE
FIGURE 6.-Distribution o f endem ic plants m Commiphora and diversity per quarter-degree grid.