High-temperature, acid-hydrolyzed remains of Polytrichum (Musci, Polytrichaceae) resemble enigmatic Silurian-Devonian tubular microfossils

Gametophytes and sporophyte components of two species of the evolutionarily early-divergent moss Polytrichum were separately subjected to high-temperature acid hydrolysis, and remains were examined by fluorescence microscopy and scanning electron microscopy. Remains included fragments of capsule, seta, leaves, stems, and calyptra. Cell walls of all remains were autofluorescent in violet and UV excitation, suggesting occurrence of resistant polyphenolic compounds. Calyptras of both species dissociated into smooth- walled, acutely branched filamentous associations of tubular cells with distinctively thickened cell junctions. In these aspects and measurements of wall dimensions made from SEMs, the hydrolysis-resistant Polytrichum calyptra remains were similar to several tubular microfossils described from Silurian and Lower Devonian deposits, whose provenance is unknown or ascribed to fungi. Our data suggest the possibility that at least some ancient tubular microfossils might have originated from Polytrichum-like early mosses. They add to increasing evidence that bryophytes left microfossil evidence for their presence millions of years earlier than is indicated by their macrofossil record.