THE MAIN BOTANICAL REGIONS OF SOUTH AFRICA.

By I. B. P. EVANS, C.M.G., M.A., D.Sc., F.L.S.,

Chief, Division of Botany and Plant Pathology, and Director of the Botanical Survey of the Union of South Africa

A part of Africa which lies south of latitude 22° falls naturally into two main botanical regions-the Cape region and the South African region. The former is of comparatively small extent and occ pies the angular strip £ country in the south-west portion of the Province of the Cape of Good Hope. The latter is of vast proportions and covers the rest of the country under review. The vegetation of the Cape region has a remarkable uniformity of character, while that of the South African region exhibits a great variety of types ranging from typical desert to tropical forest. The Cape region differs from the South African region in one important climatic factor. It experiences a winter rainfall, whereas summer rains fall over the greater part of the South African region. This difference in the seasonal distribution of the rainfall is mainly responsible for the marked dissimilarity of the vegetation in the tw regions. So different are they in aspect and composition that they have little in common and might well belong to two widely separated countries. Indeed, Bolus has well said: "The flora of South Africa cannot be treated or regarded as a whole. The diversified character of the surface of the country and the difference in the distribution and the amount of the rainfall are so considerable as to have caused corresponding important differences both in the aspect of the vegetable landscape and its systematic constituents."

THE CAPE REGION.

e region occupies the angular strip of country which is bounded by the Clitants River, the Sundays River valley, and the mountains known as the Cape ranges which form the Folded Belt. The region is commonly known to botanists as t south-western region. The country is mountainous and contains a number of deep and wide open valleys. The land rises from the coast by a seri *uccessive ranges, which from a distance appear rugged and bare, but on coser inspection reveal a wealth of most interesting plants. Snow often li n these mountain tops for many months in the year, while perennial reams, inland lakes, and vleis are of frequent occurrence. Rain f mostly during the winter months (April-September) and varies from 5-4 n. per annum, although much higher amounts are actually experienced in several localities. The general aspect of the vegetation is that of shrub or low bush varying in height from 2-8 ft. It is of a dull dark green vish hue and consists mostly of evergreen shrubs with small tougethery leaves, which not infrequently assume an oblique or perpendicular position. Below these shrubs, bulbous and succulent plants are often plentiful.

The mountain slopes are usually covered with bush and shrubs which belong to the Proteaceae, Thymeleaceae, Ericaceae, Rutaceae, Bruniaceae,

Penaeaceae, and Grubbiaceae. On the mountains in the west, the Clanwilliam cedar (Widdringtonia juniperoides) is endemic, while in the south the silver tree (Leucadendron argenteum) is typical.

On the inland valleys and plains the rhenoster bush (Elytropappus Rhinocerotis) and a great variety of plants belonging to the Restiaceae characterize the vegetation.

Along the rivers and vieis the Palmiet (Prionium serratum) and pig lily (Zantedeschia aethiopica) are typical. The region is noted for its great variety of proteas, heaths, and bulbous and tuberous plants. The general aspect of the vegetation bears a striking resemblance to that of the Mediterranean region, and for this reason it is frequently referred to as the "Cape A acchia" or "Maquis." Situated within this region between George and Knysna in a comparatively small area which experiences a fairly uniform summer and winter rainfall is a tract of evergreen forest. This must be looked upon merely as an outlier of the South African forests which occur on the south-eastern slopes of the Drakensberg range.

THE SOUTH AFRICAN REGION.

This region comprises the remainder of the country under review. It includes the greater part of South-West Africa and the Bechuanaland Protectorate, the Union of South Africa, the southern portion of Portuguese East Africa, and a narrow strip of Southern Rhodesia.

In broad outline this expanse of country consists of a great central plateau, more than 40 per cent. of which lies at an altitude of over 4000 ft. Bounding this plateau is a comparatively narrow belt of low-lying country stretching to the Atlantic Ocean on the west and the Indian Ocean on the east, while to the south it is intercepted by the chain of mountains which form the Cape ranges.

This vast region is so diversified as regards its climate, topography, and soil that several well-marked botanical provinces can be recognized. Desert types of vegetation characterize the western and southern portions of the region, where the rainfall is scanty and intermittent. Semi-deserts occur in the central portion, where the rainfall is higher, while grassland and forest cover the eastern portion, where the rainfall is more regular and the underground supplies of water more permanent.

The South African region can thus be divided into four main provinces. which may be termed :

(1) The Namaqualand Desert Province.

(2) The Karroo Province.

(3) The Kalahari Park and Bush Province.

(4) The South African Steppe and Forest Province.

(1) The Namaqualand Desert Province includes the greater part of Bushmanland, Little Namaqualand, the broad valley of the Orange River as far east as the Asbestos mountains, the greater part of Great Namaqualand, and the narrow strip of low-lying country situated between the coast and the Damaraland Highlands.

The country consists of table landscapes, vast plateaux, and arid plains. The river-beds are mostly dry throughout the greater part of the year. The soil is usually bare, stony, or sandy, while the annual rainfall varies from under 1 in. to 10 in. and increases gradually from the west eastwards.

The general aspect of the vegetation is that of widely separated xerophytic shrubs and bushes, with a fair proportion of succulent plants in the

low-lying valleys and on the rocky outcrops. Grasses do not form a conspicuous feature in the vegetation, but they occur on the high plateaux and sandy plains, where their vegetative period is short and where they are always of a tufted habit.

The Namaqualand Desert Province is characterized by the presence of Aloe dichotoma, Euphorbia virosa, E. Dinteri, Sterculia Gurichii, Cissus Crameriana, Pachypodium giganteum on the hills; Parkinsonia africana, Acacia hebeclada, A. tenax, A. hereroensis, Boscia foetida, Rhigozum trichotomum, Catophractes Alexandri, Sarcocaulon Burmanni, S. rigidum and Hoodia Gordoni on the plains; Euphorbia gregaria in the low-lying valleys, and along the dry river-beds Acacia giraffae, Acacia albida, Combretum primigenum, Euclea pseudebenum, Tamarix articulata, and Sisyndite spartea.

The western or coastal portion of this area. is usually referred to as the Namib.

The Namib is a low-lying tract of country composed largely of drifting and shifting sand dunes. It is subject to more desert conditions than the rest of the Province. Some of its more typical plants are Mesembryanthemum Marlothii, Acanthosicyos horrida, Arthraerua Leubnitziae, Welwitschia mirabilis, Zygophyllum Stapfii, and Euphorbia brachiata.

Common grasses in this Province are Aristida brevifolia, A. ciliata and A. namaquensis, while in the Namib Aristida obtusa, A. sabulicola A. subacaulis, Eragrostis cyperoides, and E. spinosa are typical.

(2) The Karroo Province includes the areas commonly known to botanists as the Karroo and the Upper Karroo. The former occupies the southern portion and is a low-lying tract of country varying in height from 1000-3000 ft.; the latter comprises the northern portion and consists of wide plains lying at an altitude of 3000-6000 ft. These plains are frequently broken by table-topped hills and "spitz-kops."

The soils are mostly shallow and rock-strewn. The rainfall varies from 5-15 in. per annum and increases from the west eastwards. The country generally, except after recent rains, has a semi-desert appearance. The vegetation is composed largely of xerophytic shrubs, shrublets, and succulents. Trees are almost entirely absent except along the river-beds.

Some of the more typical plants are: Galenia africana, Melianthus comosus, Salsola aphylla, Euphorbia mauritanica, Mesembryanthemum spinosum, Aitonia capensis, Sutherlandia frutescens, Lycium afrum, Lycium austrinum, Chrysocoma tenuifolia, Pentzia incana, Othonna pallens, Arctotis stoechadifolia, and Gnidia polycephala.

In the southern portion or Karroos, succulent plants are dominant almost everywhere. Specially typical are the Cotyledons, Mesembryanthemums, Aloes, Haworthias, Gasterias, Apicras, and Pelargoniums. In the northern portion or Upper Karroo, which is subject to far greater extremes of temperature, small shrublets belonging to the Compositae are dominant.

(3) The Kalahari Park and Bush Province occupies the vast tract of country which forms the central portion of South Africa.

It includes the greater part of Damaraland, the eastern edge of Namaqualand, British Bechuanaland, Bechuanaland Protectorate, and the lowlying country in the northern and north-eastern Transvaal which is drained by the Limpopo and Olifant's Rivers.

The country, as a whole, forms a shallow basin in the interior, which is drained on the south by the Orange River and on the north-east by the Limpopo.