Stopesia alveolata gen. et sp. nov., a fossil seed of Trimeniaceae from the Lower Cretaceous Yezo Group of Hokkaido, northern Japan, is described. Stopesia alveolata differs from extant seeds of Trimenia in its well-developed endosperm and absence of antiraphal vascular bundle, while it shares such seed coat characters as the multilayered stony exotesta with an alveolate surface, a parenchymatous mesotesta, and the operculate inner integument.
