The pace of discovery of early land plant remains has broadened the temporal gap between the first appearance of microfossils and that of megafossils. Representatives of all major categories of cryptospores (monads, dyads and tetrads) as well as minute trilete spores have been recovered from Middle Cambrian sediments of terrestrial provenance (conservatively, a fifty million year gap). What clues do we have to the affinity of these microfossils? Those that have been examined so far with the TEM (Bright Angel Shale) possess a three-layered wall that surrounds each member of the unit. While this wall is morphologically comparable to that seen in some modern green algal cysts (e.g., Mychonastes desiccatus, Chlorococcales), the thickness of the individual sporopollenin lamellae differs by a factor of two. The presence of thinner fossil lamellae in somewhat younger specimens suggests that preservation is not a limitation. Comparisons with other fossil and modern sporopollenin-containing propagules as well as less equivocal cryptospore remains from the Middle Cambrian Rogersville Shale may provide some of the first clues to the possible identity of these earliest land plant pioneers.

Key words: Cambrian, cryptospores, microfossils, Paleozoic, palynology, spores