ABSTRACT

The megafossil record of early land plants is dominated by tracheophytes. The producers of the microfossils which extend much further back in the Palaeozoic remain conjectural, although spore configuration and ultrastructure suggest a bryophyte and more precisely hepatic affinity. Such guidance in interpretation of people very simple fossils, coupled with mesofossils as a new source of information, augers well for progress in elucidating bryophyte-tracheophyte interrelationships. Enigmatic fragments appear in microfossil assemblages in the Ordovician; sheets of cuticle are known from the Caradoc, smooth tubes from the Ashgill and tubes with internal annular and spiral thickenings from the Llandovery. The chapter reviews the evidence for this hypothesis, and presents limited data on the morphology and anatomy of the spore producers. Researches have demonstrated a surprising diversity in presumed waterconducting cells when compared with extant 'pteridophytes' although few have been subjected to the same scrutiny by scanning electron microscopy as the fossils.