Plant species of the alpine zones of the tropics, particularly in the southern hemisphere, are taxonomically related to the southern hemisphere temperate zone and antarctic floras. There are interesting convergences in lifeforms between the alpine flora of the Old World and New World tropics and, indeed, between some animal taxa, too. For example, the hummingbirds (Trochilidae) of the high Andes have their counterpart in East Africa in the sunbirds (Nectarinidae).
For all the similarities, there are also distinct differences between the mountain zones of South America and of East Africa reflecting the very different geologic history of the two continents. The Andean Cordillera of South America is a continuous range of mountains stretching along the entire west coast of the continent, the result of mountain building associated with continental drift. In east African a disjunct chain of mountains ranges from Ethiopia to South Africa. Individual peaks and ranges have different ages, origins, and geologies. Instead of forming a long corridor as the Andes do, Africa's mountains are more or less islands onto themselves. Thus we will examine each continent's tropical mountain vegetation separately.