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Why are bryophyte fossils difficult to identify with certainty?

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Thick green bryophyte moss covers the trunks of three oak trees in a forest, with fallen leaves on the ground. — bryophyte Bryophyte moss growing on oak trees.

The fossil record of bryophytes is considered poor, making the identification of these specimens difficult and often insecure for several key reasons:

Absence of diagnostic features: Nearly all fossil material lacks essential reproductive structures, such as sex organs and attached sporophytes, which are critical for precise classification.1
Morphological similarity to other plants: The gametophytes of certain living vascular plants can closely resemble the gametophores of various bryophytes, leading to potential misidentification.1
General preservation challenges: While some specimens are well-preserved and show significant cellular detail, the lack of consistent, unambiguous diagnostic traits in older geological strata complicates the assignment of these fossils to specific bryophyte groups.1

Exceptions exist, such as fossils preserved in Eocene amber, where detailed cellular structure and morphology allow for more secure genus determination. However, for many other periods, precise attribution remains a challenge for paleobotanists.1