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.