Published molecular clock data suggest that land plants originated perhaps 700 mya, in the Precambrian. In contrast, the earliest fossils widely accepted as land plant remains are mid-Ordovician (450 million years old) spore aggregates. Resistant properties of liverwort gemmae suggest a possible explanation for this discrepancy. Since molecular and other data indicate that modern liverworts represent an early-diverging lineage of land plants, a survey of the acid hydrolysis (acetolysis) resistance of several liverwort species was conducted as an assessment of tissue fossilization potential. The multicellular, “smooth” gemmae produced in flask-shaped epidermal structures of the early-diverging Blasia pusilla survived. Gemmae cell walls were autofluorescent in violet and UV excitation both before and after exposure to acetolysis, suggesting the presence of wall-bound phenolic compounds. These results suggest that Blasia smooth gemmae have high fossilization potential. Blasia gemmae remains resemble microfossils described as colonial algae. Blasia is a common inhabitant of moist soils and rocky detritus in “difficult” cool-temperate to low-arctic habitats where asexual reproduction contributes to its “superfertility” and high colonization potential. Gemmae may allow reproduction when the availability of liquid water limits sexual spore production. Blasia may thus model hypothetical very early land plants that relied more on asexual than sexual reproduction in response to environmental stress. Such plants might have left remains primarily in the form of resistant gemmae that have not previously been recognized as land plant remains.

Key words: Blasia pusilla, gemmae, liverwort, microfossil