ABSTRACT
There is considerable fossil evidence that land plants originated in the Ordovician at least 475 MYA.[1,3,5] Wellman et al.[6] reported the presence of spore-containing plant fragments in Ordovician rocks from Oman. This fi nding is important because for the fi rst-time spores (microfossils) that suggested an Ordovician origin of plants were associated with macroscopic plant fossils. In fact, the spore wall ultrastructure of these new fossils shows some similarity to extant liverworts. These data provide conclusive evidence that land plants existed at least 475 MYA and suggest that liverworts may be the most basal (earliest diverging) group of land plants (for more details, see further).
