Abstract Miospore assemblages recovered from marine Upper Kimmeridgian and Portlandian and from nonmarine and lagoonal Purbeck Beds (which span the Jurassic‐Cretaceous boundary) in Dorset and Sussex are dominated numerically by Classopollis and/or Inaperturo‐pollenites and show a progressive diversification of species with time. Three microfloral suites containing a total of 77 species are recognized. Each suite is characterized by the entrance of new forms and by the frequencies of constituent species. The oldest suite is dominated by coniferalean pollen with less frequent pteridophyte spores and rare cycadalean pollen. The succeeding suites record a progressive diversification of pteridophyte and bryophyte spore types which are not, however, as abundant as coniferalean pollen. The over‐all species composition of the suites is believed to be controlled by evolutionary or large‐scale phytogeographic factors; but the detailed composition of each assemblage is controlled, in part, by local ecological‐enviro...