Description: This article discusses the biodiversity of southernmost forests and tundra ecosystems. The definition of conservation priorities for biodiversity often focuses only on the numbers of vertebrate animals and seed plants in the northern hemisphere or in the tropics. But what about the other organisms, and the more extreme regions of the world, where the species richness of flowering plants and mammals is low? An interdisciplinary team of US, UK and Chilean taxonomists, ecologists, and philosophers explored the world's southernmost forest and tundra ecosystems to estimate the diversity of the dominant vegetation, namely tiny bryophytes and lichens growing on trees, soils and rocks.