Cryptospore tetrads and dyads have been recovered from Middle Cambrian strata in Arizona (Bright Angel Shale) and eastern Tennessee (Rogersville Shale). Although many tetrads are irregular in their configuration, small tetrahedral tetrads similar to Tetrahedraletes grayae strengthen the likelihood that these are meiotic tetrads from spore-bearing embryophytes. It is now possible to trace a cryptospore history from the Middle Cambrian to the Devonian. Late Cambrian tetrads are known from at least three sites in North America. The Cambro-Ordovician record in Europe and North Africa is characterized by the monads, Attritasporites and Virgatasporites. Middle Ordovician deposits in Saudi Arabia and the Prague Basin contain dyads, tetrads and other cryptospores, including spore clusters and cuticle-like fragments. The Caradoc is marked by evolutionary stasis, based on Charles Wellman’s study of the type region in the UK. Uppermost Ordovician and lower Silurian strata contain diverse and widespread cryptospore assemblages. Cryptospores continue to diversify through the Homerian (middle Silurian) origin of tracheophytes and decline in abundance in the Early Devonian as trilete spores begin to dominate terrestrial assemblages. Although some membrane-enclosed cryptospores have been attributed to possible freshwater chlorophytes that have strayed into estuarine waters, the bulk of morphological evidence points clearly to an embryophytic affinity for these fossils. The affinities of even the earliest cryptospore tetrads are with hepatics and anthocerophytes. Since rhyniophytoids are the only plants (living or extinct) known to produce dyads normally in sporangia, dyads also stand as a proxy for the embryophytes. (To propose otherwise requires the retention of dyad sporogenesis from a hypothetical charophycean ancestor.) Thus, cryptospores continue to serve as a proxy for early land plants that have yet to reveal a macro or mesophyte record. It now seems plausible that embryophytes occupied terrestrial habitats throughout the entirety of the Paleozoic.

Key words: Cambrian, cryptospore, dyad, origin of land plants, palynology, plant evolution