''Spongiophyton'' was a thallose

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

of the early to mid-

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

, which is notoriously difficult to

classify Classification is the activity of assigning objects to some pre-existing classes or categories. This is distinct from the task of establishing the classes themselves (for example through cluster analysis). Examples include diagnostic tests, identif ...

. ''Spongiophyton'' displayed dichotomous branching, and a flattened/elliptical cross section with a thick (20–80 μm) upper cuticular surface.Fletcher (2004) It is also perforated with pores resembling those of some liverworts. It probably grew on the banks of rivers. ''Spongiophyton'' has been mistakenly interpreted as tree resin and lycopod cuticle, and was later identified as the cuticle of a thalloid plant. It has most recently been interpreted on morphological and isotopicJahren ''et al.'' (2003) grounds as a

lichen A lichen ( , ) is a hybrid colony (biology), colony of algae or cyanobacteria living symbiotically among hypha, filaments of multiple fungus species, along with yeasts and bacteria embedded in the cortex or "skin", in a mutualism (biology), m ...

—which would place it with '' Winfrenatia'' among the earliest known representatives of this group.Retallack (1994) suggested that the

Ediacaran biota The Ediacaran (; formerly Vendian) biota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period (). These were enigmatic tubular and frond-shaped, mostly sessile, organis ...

were lichens, but has since refined this hypothesis (Retallack, 2007). The significance of the isotopic data has, however, been called into question. Jahren ''et al.'' argued that

moss Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...

es and

liverworts Liverworts are a group of non-vascular plant, non-vascular embryophyte, land plants forming the division Marchantiophyta (). They may also be referred to as hepatics. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in wh ...

had a signature of under ‰, and lichens were exclusively > ‰. But in deducing this they relied solely on their own data, neglecting to include published datasets or

bryophyte Bryophytes () are a group of embryophyte, land plants (embryophytes), sometimes treated as a taxonomic Division (taxonomy), division referred to as Bryophyta ''Sensu#Common qualifiers, sensu lato'', that contains three groups of non-vascular pla ...

s from a wide range of habitats. They also failed to take into account any adjustment necessary to overcome post-burial alteration of the , or to compensate for the different isotopic composition of the early Devonian atmosphere. Repeating Jahren's experiments with these factors taken into account shows that most major groups' values overlap significantly, and do not provide a statistically significant case for the inclusion of ''Spongiophyton'' in any group.

Notes

References

* * * * * Devonian life Paleozoic life of Ontario Paleozoic life of New Brunswick Paleozoic genera {{devonian-plant-stub