Trinity College Dublin

Skip to main content.

Top Level TCD Links


300 Years of Growth

Wallace's Line and plant distributions: two or three phytogeographical areas and where to group Java?

17 June 2011

Alfred Russel Wallace is one of the most famous biologists of all time. Known for his co-discovery with Darwin of the Theory of Evolution by Natural Selection he is also famous for his discovery of large scale patterns in the fauna of SE Asia AKA Malesia. Wallace was the first person to realise that the animals in the east of Malesia differed substantially from those in the west. For example, in the east are non-placental marsupials such as the kangaroo, whilst these are replaced in the west by placental mammals such as bears. Wallace realised that a line running more or less north to south would delimit these areas. His line defines a boundary which divides Malesia in two and which indicates the limits of distribution for animals living to its east and west. In other words, animal species are distributed either to the east or west of the line – rarely crossing it. Wallace’s line remains the best known and most important biogeographic division known – it is a textbook classic.

Subsequently, other workers have confirmed the occurrence of this line though there has been some dispute as to where exactly it might be placed. However, surprisingly no workers up till now have looked at plants to see whether their distributions follow Wallace’s line or not.

In a recent paper, just published online in Biological Journal of the Linnean Society, workers in the School of Natural Sciences, TCD, Leiden University and the Chinese Academy of Sciences analysed the distribution of 7,340 plant species, divided over 165 families and 896 genera. This represents 25% of the estimated 30,000 species of ferns and Angiosperms in Malesia and includes all plant species which have so far been published for the Flora of that region.

The paper shows that plant distributions do not follow Wallace’s line. Rather, the analysis revealed a stronger partitioning of Malesia into three instead of two regions: the western Sunda Shelf minus Java (Malay Peninsula, Sumatra, Borneo), central Wallacea (Philippines, Sulawesi, Lesser Sunda Islands, Moluccas, with Java) and the eastern Sahul Shelf (New Guinea).

Commenting on the paper John Parnell indicates that these three new phytogeographic areas also reflect the present climatic division of Malesia as an ever-wet climate exists on the Sunda and Sahul Shelves, while most of Wallacea has a yearly dry monsoon. The pattern also reflects historic climatic changes as during glacial maxima the Sunda and Sahul Shelves became land areas connected with Asia and Australia respectively, while sea barriers remained within Wallacea. Consequently, the flora of the two shelves is more homogeneous than the Wallacean flora. As the analysis indicates that for plants Wallacea is a distinct area comprising many endemic, drought tolerant floristic elements there are significant implications for conservation and all future biogeographic analysis. See

The full article can be downloaded here.


Last updated 11 July 2011 by