LAUSR

Abstract A relatively rich association of six species of embryophyte plants is known from the upper Silurian of the Prague Basin (Bohemian Massif, Czech Republic). All stratigraphically controlled specimens come from the Neocolonograptus parultimus-Neocolonograptus ultimus Zone of the Přidoli. A new genus and species, Tichavekia grandis Psenicka, Sakala et Kraft, is established. The new combination Aberlemnia bohemica (Schweitzer) Sakala, Psenicka et Kraft, comb. nov. illustrates its Lycophytina affinity. The distribution and taphonomy of these plants in the Prague Basin indicates the proximity of exposed land interpreted to be islands of volcanic origin. Two local associations show primary differences in vegetated areas of the islands and apparent ecological responses of the primitive vascular plants to their habitats. Suitable environments in the coastal zones of volcanic islands in the Prague Basin, which was situated at the outer periphery of a broad Gondwanan shelf, likely represent significant transfer points for an initial dispersion and a first expansion of land plants. Repeated vegetation of the islands is inferred from the discrete distribution of land plants at different stratigraphic levels. These changes are explained partly in context of local changes of the island relief, and partly as responses to global climatic and sea level fluctuations, and fit environmental dynamics of islands of volcanic origin in general. This Initial Plant Diversification and Dispersal Event (IPDDE) is of considerable significance in the evolution of plants documented from the Bohemian Massif.