Antarctic cryptogamic communities are often remarkable for their uniformity in vegetation structure and floristic composition. Many typically exist as closely related units of vegetation in a continuum of variation which com- prises an ecological mosaic of communities. Thus, specific associations of species tend to occur wherever a similar suite of environmental criteria prevails. However, many individual species are sensitive to minor differences in edaphic and micro- climatic features of the habitat. This is commonly expressed in terms of sharp changes in species dominance and in community structure. The spatial dynamics of the vegetation is illustrated for the Site of Special Scientific Interest (SSSI) on Bailey Peninsula near Casey Station, Wilkes Land. Here, there exist some of the most extensive and best-developed plant communities in continental Antarctica. The vegetation associated with various topographical features was analyzed in contiguous quadrats along transects and its composition related to soil moisture, soil chemistry, and microclimate. The change in the distribution and abundance of the principal bryophyte and lichen species along these environmental gradients reflects their ecological requirements and tolerances.