The eastern rainforest is a treasure chest for naturalists as it supports the greatest number of animal and plant species in Madagascar. To visitors more familiar with temperate woodlands, where one or two species like beech or maple dominate, the diversity of plants in a small area of tropical rainforest is bewildering. In Madagascar botanists are still classifying the flora: palm specialists have recently discovered many new species, and orchids, for which the island is famous, are also receiving considerable attention. Evergreen rainforest in Madagascar has different characteristics depending on altitude and rainfall. Most of the protected areas described here fall into the two categories outlined below. Lowland rainforest lies below 800m and is drenched with an average 3,500mm of rain per year. It is similar to rainforest growing in other tropical regions, with large trees supported by buttress roots, smaller trees with stilt-like aerial roots, saplings, lianas, epiphytes and ferns. Compared with other continents, however, the trees are closer together and the canopy lower, and there are fewer tall trees poking their crowns above the rest.

Species of Impatiens are common here. Montane rainforest is typical of key reserves like Andasibe-Mantadia (Périnet), Ranomafana and Montagne d'Ambre (Amber Mountain). It is found between 800m and about 1,300m, above which it is called high altitude montane forest. Tree ferns are a feature of montane forests and bamboo is common, as are species of Kalanchoe . Compared with lowland rainforest, leaves are smaller and tougher, mosses and epiphytes are more abundant, and shrubby undergrowth flourishes as more light reaches the forest floor.