The Coast Regions
To begin with the Namib. The general aspect of the vegetation here is monotonous, since there are but few plants that rise to any appreciable height from the sandy surface to break the dull level. No tree grows within a dozen miles of the coast, except in an occasional watercourse where there is underground moisture.
The Kokerboom, Aloe dichotoma, however, often occurs as a solitary tree, and occasionally forms little groves on the limestone hills of the eastern portion of the Namib. In the winter, when they bear large clusters of bright yellow flowers, they give quite a touch of colour to the drab landscape.
The northern Namib has two plants of singular interest in the Welwitschia and the Naras. The Welwitschia, Welwitschia Bainesii, is in reality a tree with a fairly thick trunk that terminates abruptly just above the ground. Two thick, leathery leaves are permanent and grow continuously at their base until they sometimes reach a length of 10 feet, by which time they are frayed into numerous snake-like thongs. The plant flowers in January and the cones ripen in May. The roots of the largest plants may be traced to a very great depth in the sand. “This plant,” says Dr. Marloth,[5] “is of great scientific interest, being the most highly developed gymnospermous plant known to us either in the living or the fossil state. It is not a connecting link between the gymnosperms and the angiosperms, but the final stage of a separate line of development of the vegetable kingdom, that, as far as is known to us, led no further.” The Welwitschia was first discovered by Dr. Welwitsch in Southern Angola in 1865. It has not been found south of the Kuisip district.
The curious Naras, Acanthosicyos horrida, has been well termed the “Wonder of the Waste,” for this shrubby, leafless member of the order Cucurbitacea spreads over the sand dunes in dense straggling masses, defying all the sandstorms that threaten to bury it. Instead of tendrils it bears sharp thorns, while the main root may be as thick as a man’s arm, with a length of 20 to 40 feet. The fruit is about the size of a very big orange, and the skin encloses a yellow pulp of a rich flavour and a number of seeds similar in taste to almonds. The fruit is greatly relished by the natives, and, as it has extraordinary nutritive value, they almost live on it. The seeds are stored for the dry season, when no fruit can be obtained. The existence of this plant always indicates underground moisture. Both the Welwitschia and the Naras flourish in the vicinity of Walvis Bay, but the Naras has been found in recent years in several places in the southern Namib. It is believed that the species does not occur naturally so far south, but has been introduced by natives. Its true southern limit is not far from the southern extremity of Walvis Bay.[6]
In the region described as the Upper Kuisip Zone, which embraces the valley of the Kuisip, among the fairly abundant vegetation, with camelthorns, ebony trees, and wild figs, the handsome Ana tree, Acacia albida, is found. The fruit of this remarkable tree is a legume. The beans, when ripe and dry, are used for fodder for cattle, and they have extraordinary fattening properties. Cattle also relish the leaves of the tree.
The flora of the desert south of Luderitzbucht is much poorer than that of the northern portion, and, as Schinz points out, the difference is probably accounted for by the presence of a more copious supply of underground water in the northern area. But the Namib has a richer vegetation than is generally supposed.
“As an illustration,” writes Dr. Marloth, who made a careful examination of the Lower Namib in 1909, “it may be mentioned that I have observed over twenty species of Mesembrianthemum, five species of Pelargonium (mostly shrubby), two of Sarcocaulon, three of Lycium, two of Zygophyllum, two of Salsola, three of Othonna, five shrubby Leguminosæ (Lebeckia and Crotalaria), five species of Euphorbia, and many other genera represented by one or two species.”[7]
He distinguishes four formations according to the nature of the ground: the seashore, the sandy plains, the rocky hills, and the gravel-covered flats of the rising plains beyond the coast-belt; and we cannot do better than adopt his convenient division.
The seashore.—The sand dunes are devoid of vegetation on account of the ever-shifting nature of the sand, and they present an unforgettable scene of sterility and dreariness. A few plants specially adapted to salt water, such as Salicornia natalensis and Bassia diffusa, are found in the shallows or around the lagoons.
The sandy plains and dunes.—Further inland Salsola Zeyheri is common. This low, tight-looking shrub, grey in colour, about 2 to 3 feet in height, has considerable value, since it forms good food for the camels used for transport purposes. Coarse dune-grasses are found in sheltered patches. The Mesembrianthemum is a characteristic Namib plant; it grows on rocks as well as sand.
The rocky hills.—Here we find a more varied vegetation. The well-known Kokerboom (Aloe dichotoma) is a conspicuous feature. It is interesting to notice that the name Koker or Quiver (D. koker, a case sheath; G. Kocher, a quiver) was given to this tree because the Bushmen and Hottentots used the pithy branches to make quivers for their poisoned arrows.
Even more numerous than the Aloe dichotoma are several species of Euphorbia. Schinz, it may be noted, has described the eastern edge of the desert as a Euphorbia-steppe.[8] The E. gummifera is, perhaps, the most noticeable plant, and in the Garub region this species abounds. It forms compact bushes, 3 to 6 feet in height, and its grey twigs have rather an unpleasant scent, while they contain an unusually rich supply of milk juice. The E. cervicornis, the olifant melkbosch of Little Namaqualand, is found occasionally. A little plant that crouches behind rocks or isolated stones is the dwarf shrublet Pteronia succulenta, whose main stem is often bent over at a right angle by the fierce winds as soon as it pushes its head above the shelter. Other plants, usually forming upright bushes, are here compelled to bend before the strong winds; notable among these is the Pituranthus aphyllus, a leafless umbellifer.
A plant of peculiar interest found among the many species of Mesembrianthemum is the M. rhopalophyllum, which is remarkable for its highly-specialised window-leaves. “The plant grows embedded in the sand, nothing but the flat, slightly convex apex of each leaf being visible, and even that is covered with more or less sand according to locality. While the leaf itself is fresh green with a rather delicate skin, the exposed part is protected by a thick epidermis and cuticula, and possesses comparatively few stomata. It is through this portion, which has the functions of a window, the leaf receives its light, being thus illuminated from within. There are five to ten, or even more, leaves to each plant, but nothing appears at the surface except these windows; they peep out of the sand like the eyes of the sand-lizard or sand-vipers, which often hide themselves in a similar way.”[9]
It is very curious to see the short flowers of these plants in the spring, for they grow, apparently, straight out of the sand. Only on investigation are the leaves and stem discovered. The leaves are club-shaped. Nature has evidently chosen this underground mode of existence for the plant in order to protect it against the herbivorous animals. These interesting plants are found only in Africa.
The leaves of the Augea capensis are very strong in sap, but the plant is so salty that even the camels will turn away from it. This plant is found in many parts of the Karroo.
An untidy-looking shrublet, the Sarcocaulon rigidum, is fairly abundant. A peculiarity of its structure is the sharp-pointed spines, which are specially modified stalks of former leaves. Leaves of vivid green cover these plants in the spring, and at times they are numerous enough to influence the colour of the landscape. Pink flowers appear on them in October.
The gravel plains.—The rising plains of the inner Namib, which have an altitude of 1,800 feet, some fifty miles from the coast, are swept by furious sand-laden winds for the greater part of the year. The sea-fogs rarely reach these areas, and, as the rainfall is a negligible quantity, no sign of life may be encountered for many miles, only a vast, monotonous waste of gravel and sand meets the eye. Occasionally one lights upon the typical Sarcocaulon rigidum, the Candle-bush or Bushman’s candle. This plant has been specially adapted to meet the conditions of the desert, and it is able to defy the hottest sun and the fiercest sandstorms. Layers of corky tissue, impregnated with a mixture of fat, wax, and resin, form the bark. This horny casing is the plant’s armour against the attacks of its enemies. It burns steadily like a wax candle with a yellow, smoky flame, even when cut fresh from the ground.