The Tremadoc to early Llanvirn is the time interval in the Ordovician for which a global acritarch distribution pattern can be proposed. It is possible to differentiate a high latitude, cold- to temperate-water realm and a low latitude, warm-water realm. The cold-water assemblages, recorded from numerous localities at the northern border of Gondwana in the southern hemisphere, include some diagnostic morphotypes, such as Arbusculidium filamentosum, Arkonia, Aureotesta, Coryphidium-Vavrdovella, Dicrodiacrodium, Frankea and Striatotheca. Assemblages related to warm-water areas are described from Canada, the United States, northern China, Australia, and Baltica. Although a distinction of separate provinces within the cold-water and warm-water realms is difficult, the differentiation between these two units appears evident and a distinction of the assemblages from peri-Gondwana and the microfloras from Baltica is possible. This enables a recognition of the Trans-European Suture Zone in the early to middle Ordovician.