THE INDO-MALAYSIAN NORTH-AUSTRALIAN PHYCOGEOGRAPHICAL REGION REVISED

The present knowledge of the freshwater algal flora in the Indo-Malays ian North Australian region is reviewed. More than 4700 taxa have been recorded from this region. Desmids, diatoms and cyanobacteria are amo ng the better studied groups of organisms, while phytoflagellates have received very little attention. Phytoplankton communities in tropical lakes are generally similar to summer communities of temperate lakes. In addition, there is a large number of typical tropical taxa, includ ing pantropical and regional endemic elements. Local endemism occurs i n the old Tertiary lakes of the region. The composition of algal commu nities changes markedly along an altitudinal gradient, and tropical ta xa are gradually replaced by taxa characteristic for cool climatic con ditions. Biogeographical distribution patterns are exemplified for the desmids and diatoms. Among the more than 2680 desmids recorded from t he Indo-Malaysian North Australian region, about 800 have never been f ound elsewhere. Dispersal by migratory birds and past climatic changes might explain distribution patterns. Because of incomplete taxonomy a nd a general lack of understanding of the autoecology, distribution an d speciation of freshwater algae, however, there remain serious obstac les for detailed biogeographical analyses.