The natural history of Africa encompasses some of the well known megafauna of that continent. Natural history is the study and description of organisms and natural objects, especially their origins, evolution, and interrelationships. Flora The vegetation of Africa follows very closely the distribution of heat and moisture. The northern and southern temperate zones have a flora distinct from that of the continent generally, which is tropical. In the countries bordering the Mediterranean, there are groves of orange and olive trees, evergreen oaks, cork trees and pines, intermixed with cypresses, myrtles, arbutus and fragrant tree-heaths. South of the Atlas Range the conditions alter. The zones of minimum rainfall have a very scanty flora, consisting of plants adapted to resist the great dryness. Characteristic of the Sahara is the date palm, which flourishes where other vegetation can scarcely maintain existence, while in the semidesert regions the acacia, from which gum arabic is obtained, is abundant. The more humid regions have a richer vegetation; dense forest where the rainfall is greatest and variations of temperature least, conditions found chiefly on the tropical coasts, and in the west African equatorial basin with its extension towards the upper Nile; and savanna interspersed with trees on the greater part of the plateaus, passing as the desert regions are approached into a scrub vegetation consisting of thorny acacias, etc. Forests also occur on the humid slopes of mountain ranges up to a certain elevation. In the coast regions the typical tree is the mangrove, which flourishes wherever the soil is of a swamp character. The dense forests of West Africa contain, in addition to a great variety of hardwoods, two palms, Elaeis guineensis (oil palm) and Raphia vinifera (bamboo palm), not found, generally speaking, in the savanna regions. Bombax or silk-cotton trees attain gigantic proportions in the forests, which are the home of the India rubber-producing plants and of many valuable kinds of timber trees, such as odum (Chlorophora excelsa), ebony, mahogany (Khaya senegalensis), Oldfieldia (Oldfieldia africana) and camwood (Baphia nitida). The climbing plants in the tropical forests are exceedingly luxuriant and the undergrowth or "bush" is extremely dense. In the savannas the most characteristic trees are the monkey bread tree or baobab (Adansonia digitata), doum palm (Hyphaene) and euphorbias. The coffee plant grows wild in such widely separated places as Liberia and southern Ethiopia. The higher mountains have a special flora showing close agreement over wide