Centres of Development and Patterns of Distribution of the Family Melastomataceae in Indo-Malesia

1.The Melastomataceae is a homogeneous family of about 220 genera and 5300 species and is generally confined to the tropical and subtropical regions, avoiding arid conditions and attaining prolific developments in the rain forests between the tropic of cancer and the tropic of capricorn. More than one half of the World's melastomataceous genera (about 120) and two-thirds of the total number of species (about 3353) are confined to the New World. The melastomataceous flora of Indo-Malesia consists of 64 genera and about 1300 species. In the Old World the incidence of melastomataceous species for Indo-Malesia and Africa is in the ratio of 2:1.

2.The present distribution of Melastomataceae in both the New World and the Old World is discussed on the basis of Wegener's hypothesis of "Continental Drift". Instead of considering the island of Madagascar as the centre of origin of the family in a restricted way, it is considered that "Gondwanaland" was ideally suited for the melastomataceous flora and those blocks that moved away after the breaking up of this huge continental mass in the Late Cretaceous, each carried their own share of melastomataceous species which, after gradual establishment in new situations during a long span of time and space, proliferated into several new taxa by an intensive process of evolution.

3.The Deccan Peninsula + Ceylon block in drifting over the Indian Ocean must have carried the original Gondwanaland stock and gene-pool of the Melastomataceae which later-when this block was fused with Laurasia and the Tethys Sea had disappeared-became the centre of development of the family in continental Asia. Then Melastomataceae could further develop on the southern part of Laurasia and from there migrate eastward to the Malesian islands, the Western Pacific and northern Australia.

This implies the conclusion that, though Australia also formed part of the ancient Gondwanaland, this cannot have carried part of the ancient Gondwanaland Melastomataceae when Australia drifted apart.

4.An attempt has been made to assess the centres of distribution of Indo-Malesian Melastomataceae and from this study the following four centres of development are proposed : (i) The Deccan-Ceylon centre, (ii) The Himalayan-Yunnan centre, (iii) The Sunda centre and (iv) The Philippine-Papuan centre.

5.The Island of Borneo is unique in having the largest number of genera-42 out of the Indo-Malesian total of 64 genera-and the largest number of species i.e. 257. Perhaps, it is due to the part played by the mountain of Kinabalu in enriching the floristic composition of Borneo. It is generally considered by phytogeographers that Kinabalu is a great sanctuary of flora, past and present, and a nursery of endemic elements.