The principal islands are Aitutaki, Atiu, Mangaia, Manuae, Mauke, Mitiaro, Palmerston, Rarotonga, and Takutea.

Rarotonga is the highest of the islands, with the deeply-eroded, steep-sided volcanic cone Te Manga (652 metres elevation) at its center.

[1] Mitiaro, Atiu, Mauke, and Mangaia went through a long geologic cycle of erosion, subsidence, and emergence followed by uplift in the Tertiary era.

Each has central eroded volcanic hills, reaching an elevation of about 100 metres, surrounded by a belt of uplifted ancient coralline limestone, known as makatea, up to 2 km wide.

Fagraea berteroana and the endemic Fitchia speciosa are the predominant trees, and both have massive and extensive roots which provide support and stabilize the rocky slopes.

Other common trees include species of Homalium, Canthium, Alyxia, Coprosma, Meryta, and Metrosideros.

[1] On Mitiaro, Atiu, Mauke, and Mangaia, the native vegetation of the central areas of volcanic soil have been almost completely replaced with introduced plants.

Patches of forest occur inland, with species of Pisonia, Guettarda, and Pandanus, and introduced coconut palms (Cocos nucifera).

Predation by the African ant Pheidole megacephala, introduced in the 1870s, has driven 11 of Rarotonga's 13 endemic land snail species to extinction.

[2] Te Manga Nature Reserve preserves most of Rarotonga's remaining cloud forest area above 400 metres elevation.