Papuasia

Papuasia covers New Guinea, the Bismarck Archipelago, and the Solomon Islands — the eastern half of the Indo-Australian archipelago. New Guinea is the world's second-largest island and the largest tropical island; running down its spine is a continuous mountain chain, the Central Range, which carries the highest non-Andean equatorial peaks. Puncak Jaya in Indonesian Papua reaches 4,884 metres, with Mount Wilhelm (4,509 m) and Mount Giluwe (4,367 m) close behind. Until recently these summits held the only equatorial glaciers on Earth — now almost gone, but still mapped on older atlases.

The climate is equatorial and wet, with monsoon variation south of the Central Range and a rain-shadow savanna in the Trans-Fly lowlands of southern New Guinea. Almost the whole region is rainforest in some form. Lowlands carry tropical evergreen rainforest with Lauraceae, Myrtaceae, Sapotaceae, and Anacardiaceae giants; vast mangrove forests fringe the Fly and Sepik deltas; and the Trans-Fly lowlands hold the only large lowland savannas of the region, with Eucalyptus and Melaleuca. Above about 1,500 metres the forest shifts into montane oak-conifer mosaic, then mossy cloud forest where every branch, trunk, and rock is layered in epiphytes — Vireya rhododendrons, miniature Dendrobium, Coelogyne, and Bulbophyllum orchids, Vaccinium, and tree-ferns.

The flora is exceptional. A 2020 census led by Rodrigo Cámara-Leret confirmed New Guinea as the most plant-diverse island on Earth, with about 13,634 vascular plant species and roughly 68% endemism. Orchidaceae alone tops 3,000 species. Rhododendron section Vireya — the tropical rhododendrons — reaches its global diversity centre here with more than 300 species, most of them epiphytic on cloud-forest trees. Familiar terrarium genera (Alocasia, Schismatoglottis, Rhaphidophora, Hoya, Aeschynanthus, Begonia, Asplenium, Microsorum, Bolbitis, Cyrtandra) all have major radiations in Papuasia.

The region is also a centre of agricultural origin. Banana (Musa) and sugarcane (Saccharum officinarum) were independently domesticated in the New Guinea highlands, and the UNESCO-listed Kuk Swamp site holds some of the earliest known evidence of agriculture anywhere on Earth.