Wallace's line and the distribution of the liverworts of Sulawesi

We explore the significance of Wallace's line as a biogeographical boundary in wind-dispersed organisms based on a phytogeographical analysis of the liverworts of Sulawesi. We analysed the geographical and elevational ranges and dispersibility of 177 species of liverworts, including 44 new to Sulawesi. The majority of the species proved to be widespread in the Malesian archipelago; only two are endemic to Sulawesi. Thirteen species (7.5%) belong to the eastern Malesian element, having their westernmost border in Sulawesi. In contrast, only two are western Malesian in distribution, reaching eastwards to Sulawesi. Widespread species occur both in lowland and montane regions; those with eastern Malesian ranges are largely restricted to montane areas. Poor dispersibility (spores unisexual, asexual reproductive devices lacking) is highly characteristic of the eastern Malesian species. We conclude that the greater number of eastern than western Malesian liverwort species in Sulawesi (13 vs 2) is in support of Wallace's line and indicates that this border of Asiatic and Australasian biogeographic regions is also relevant to wind-dispersed organisms such as liverworts. The limited availability of suitable habitats and reproductive constraints of the eastern Malesian species may have impeded their migration westwards across Wallace's line.