Nematothallus is the name given by Lang (1937) to ancient assemblages of two types of tubes occurring together with “cuticle” and spores, which he thought represented an extinct group of land plants intermediate between algae and vascular plants. Microfossils attributed to Nematothallus have since been found in Ordovician to Lower Devonian deposits. Some authorities limit the name Nematothallus to assemblages of tubes; others have given the name Cosmochlaina to ornamented “cuticles” of the Nematothallus type. Since molecular and other evidence identifies modern liverworts as an early-diverging group of land plants, we subjected a variety of liverworts—Blasia pusilla, Lunularia sp., Ricciocarpos natans, Preissia sp., and Marchantia polymorpha—to standard high temperature acid hydrolysis (acetolysis) or rotting in moist soil for at least 3 months. The lower epidermis of M. polymorpha survived acetolysis as cellular scraps bearing stubs or short lengths of rhizoids, and rotting as larger expanses of tissue attached to numerous rhizoids of more than one type. These resistant tissues were autofluorescent in UV and V excitation both before and after acid or soil exposure treatments, suggesting occurrence of phenolic wall polymers. Resistance of lower epidermal tissues and rhizoids, which are in close contact with soil decay microbes, may be adaptive. Ornamentation of the M. polymorpha lower epidermis remains resembled that of fossil “cuticles” described as Cosmochlaina. This evidence suggests that Cosmochlaina could be epidermal remains of a M. polymorpha-like liverwort, and that Nematothallus may also be the remains of early liverworts having resistant-walled rhizoids and/or epidermal surfaces.

Key words: Marchantia polymorpha, Cosmochlaina, epidermis, microfossils, Nematothallus, rhizoids