The first fossil representatives of the modern Osmundaceae (= tribus Osmundeae) include rhizome fossils with "Claytosmunda"-anatomy or with structural features characteristic for "Osmundastrum cinnomomeum" and its precursors. The same holds for the equally old leaf fossil record of the group. The main diagnostic feature of Osmundeae (modern Osmundaceae) is a heterogenous sclerenchymatic ring in the stipe basis. This potential synapomorphy is the only character differentiating between Osmundeae and the paraphyletic genus collecting their potential early ancestors and sister lineages, "Millerocaulis". The basic "Bauplan" shared with 'Millerocaulis' was generally kept within the Osmundeae-lineage and only slightly to moderately modified in the last 200 million years. Triassic-Jurassic rhizome and frond morphologies remained essentially unaltered in the lineage leading to "Claytosmunda claytoniana". This makes it impossible to discern direct ancestors of "C. claytoniana" from the ancestors of its sister lineages "Osmunda" and "Plenasium"), or their shared ancestors. Molecular dating placed the split between "Osmunda" and "Plenasium", and their divergence from "Claytosmunda" in the Early Cretaceous, co-eval with the divergence between the sister genera "Todea" and "Leptopteris". The "Osmundastrum"-lineage diverged much earlier (probably Middle Triassic), which fits with the new classification of re-evaluated rhizome fossils originally included in "Millercaulis". A comprehensive list of rhizome and leaf fossils associated with modern Osmundaceae (Osmundeae in the classification of Bomfleur et al.) can be found at datadryad.org.