thumb|upright=1.2|Map 1: A very broad definition of Malesia includes both the [[World Geographical Scheme for Recording Plant Distributions's Malesia (green) and most of its Papuasia (orange).]]
Malesia<!--NOT A TYPO, DO NOT 'CORRECT'--> is a biogeographical region straddling the Equator and the boundaries of the Indomalayan and Australasian realms. It is a phytogeographical floristic region in the Paleotropical kingdom. It was first recognized as a distinct region in 1857 by Heinrich Zollinger, a Swiss botanist and explorer. The precise boundaries used to define Malesia vary. The broadly defined area used in Flora Malesiana consists of the countries of Malaysia, Singapore, Indonesia, Brunei, the Philippines, Timor-Leste and Papua New Guinea. Van Steenis defined the area of Malesia through the concept of 'demarcation knots': lines across which there are major changes in the genera present in the flora. There were three clear boundaries: between the Malay Peninsula (including part of southern Thailand) and mainland Asia (line 1 in map 2); between the Philippines and Taiwan (line 2 in map 2); and along the Torres Strait between New Guinea and Australia (line 3 in map 2).
The first edition of the World Geographical Scheme for Recording Plant Distributions (WGSRPD) used the same definition, but in the second edition of 2001, New Guinea and the Bismarck Archipelago were removed from Malesia and united with the Solomon Islands, previously placed in the WGSRPD's Southwestern Pacific region, and placed into a new region, Papuasia, whose eastern boundary extends to line 5 in map 2.
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