Malesia is abiogeographical region straddling theEquator and the boundaries of theIndomalayan andAustralasian realms. It is aphytogeographicalfloristic region in thePaleotropical kingdom. It was first recognized as a distinct region in 1857 byHeinrich Zollinger, a Swiss botanist and explorer.[1] The precise boundaries used to define Malesia vary. The broadly defined area used inFlora Malesiana consists of the countries ofMalaysia,Singapore,Indonesia,Brunei, thePhilippines,Timor-Leste andPapua New Guinea.[2] The original definition by theWorld Geographical Scheme for Recording Plant Distributions (WGSRPD) covered a similar area, butNew Guinea and some offshore islands were split off asPapuasia in its 2001 version.
Definitions of Malesia:
Areas:
Malesia was first recognized as a distinct floristic region in 1857 byHeinrich Zollinger, a Swiss botanist and explorer. In 1948 and 1950,Cornelius G. G. J. van Steenis developed the idea of Malesia, and put forward plans for aFlora Malesiana.[3][4] 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 theMalay Peninsula (including part of southern Thailand) and mainland Asia (line 1 in map 2); between the Philippines andTaiwan (line 2 in map 2); and along theTorres Strait between New Guinea and Australia (line 3 in map 2).[1] The eastern boundary was less clear; van Steenis somewhat arbitrarily placed it between theBismarck andSolomon Islands and the other Pacific islands (line 4 in map 2).[5] Van Steenis initially used Zollinger's name 'Malesia'. He later anglicized it to 'Malaysia', but when the country of Malaysia was formed in 1963, it was necessary to return to the original name.[5][6]
The first edition of theWorld 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 theSolomon 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.[7]
Using theFlora Malesiana definition, Malesia has a shared tropical flora derived mostly fromAsia, but also with numerous elements of theAntarctic flora. Malesia is a hotspot of global biodiversity. In 1995, it was estimated that there were 42,000 species ofvascular plants, of which 70% wereendemic. By comparison, Europe, which is about three times the area, had 11,000 species of vascular plants, of which about 30% were endemic.[8]
Western Malesia includes the Malay Peninsula and the islands ofSumatra,Java,Bali, andBorneo (area A in map 2). It shares the large mammal fauna of Asia and is known asSundaland. These islands are on Asia's relatively shallowcontinental shelf, and were linked to Asia during theice ages, when sea levels were lower. The south-eastern edge of Sundaland (line 6 in map 2) is theWallace Line, named afterAlfred Russel Wallace, the nineteenth-century British naturalist who noted the difference in fauna between islands on either side of the line.
Dipterocarps are predominant trees in the lowland forests of Sundaland.[9] Sundaland has the greatest diversity of Dipterocarp species, with 10 to 14 native genera and approximately 450 native species, including approximately 267 species on Borneo, 155 on the Malay Peninsula, and 106 on Sumatra.[10]
The eastern boundary of central Malesia (area B in map 2) is formed byLydekker's Line (line 7 in map 2).[5] Central Malesia can be divided into two subareas: thePhilippines in the north andWallacea in the south.
The Philippines form the northern part of central Malesia. Most of the Philippines were never connected to the Asian mainland, and have a largely Asian-derived flora, and a distinct mammalian fauna.
The Philippines have approximately 50 species of Dipterocarps in 11 genera.[10]
The islands between Sundaland and New Guinea, called Wallacea, form the southern part of central Malesia. They were never linked to the neighboring continents, and have a flora and fauna that include Indomalayan and Australasian elements.
Dipterocarps, which are dominant in Sundaland, are less common in Wallacea, with only 13 species in 4 genera.[10]
As defined inFlora Malesiana, Eastern Malesia consists of New Guinea and the Bismarck Archipelago (area C in map 2).The eastern end of this definition of Malesia, which includes New Guinea and theAru Islands of eastern Indonesia, is linked to Australia by a shallow continental shelf, and shares manymarsupial mammal and birdtaxa with Australia. New Guinea also has many additional elements of the Antarctic flora, including southern beech (Nothofagus) andeucalypts. New Guinea has the highest mountains in Malesia and Papuasia, and vegetation ranges from tropical lowland forest to tundra.
In the second version of the WGSRPD, New Guinea and the Bismarck Archipelago, together with the Solomon Islands, are placed inPapuasia (areas C and D in map 2) rather than Malesia.[7]
Major contributions torainforest assembly have come from floristic elements which were carried on theIndian Plate and montane elements which have come from theAustralian Plate (Sahul). The Sahul component is now understood to include substantial two-way exchanges withSunda inclusive of lowland taxa. Evidence for the relative contributions of the great Asiatic floristic interchanges (GAFIs) with India and Sahul, respectively, to the flora of Malesia comes from contemporary lineage distributions, thefossil record, time-calibratedphylogenies, functional traits, and the spatial structure of genetic diversity. Functional trait and biome conservatism are noted features of montane austral lineages from Sahul (e.g., diversePodocarpaceae), whereas the abundance and diversity of lowland lineages, including groups such asSyzygium (Myrtaceae) and the Asiandipterocarps (Dipterocarpoideae), reflect a less well understood combination of dispersal, ecology, and adaptive radiations. Thus, Malesian rainforest assembly has been shaped by sharply contrasting evolutionary origins and biogeographic histories.[11]
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