Rhynie Spores

Fossilised spores from vascular plants are quite common in beds of the Rhynie chert and also within the finer grained interbedded sediments such as shales and mudstones. They are usually extracted from the sedimentary rocks by macerating rock samples in solutions of Hydrofluoric acid which dissolves the silica minerals in the sediment and leaves the resistant spores and other acid-insoluble organic remains for analysis (Wellman & Axe 1999). Interestingly, upon extraction the spores often appear better preserved within the mudrocks than in the cherts, though this may be a reflection of the effects of silicification and replacement of the original organic material.

Above: Apiculiretusispora sp., spore diameter approximately 40µm (Copyright owned by University of Sheffield). Above: Brochotriletes sp., spore diameter approximately 50µm (Copyright owned by University of Sheffield). Above: Dictyotriletes sp., spore diameter approximately 50µm (Copyright owned by University of Sheffield).

Many genera and species have been recognised and described, though there still remains a degree of uncertainty as to which of the known vascular plants of the Rhynie chert they can be assigned to. In situ spores have been described in the past for Horneophyton and Rhynia by Bhutta (1973a, b). There may well be spores present that are representative of other plants that have not been so far discovered in the cherts. The abundance and variety of spores present in the sequence of Rhynie sediments has been useful in terms of biostratigraphy in determining the age of the rocks (Wellman 2004).   The images to the left and right display a few of the spore types or palynomorphs that have been found.   The study of the fossil spores or palynology of the Rhynie chert and sediments is ongoing at the University of Sheffield.

Above: Emphanisporites sp., spore diameter approximately 60µm (Copyright owned by University of Sheffield). Above: Retusotriletes sp., spore diameter approximately 40µm (Copyright owned by University of Sheffield). Above: A zonate spore, diameter approximately 50µm (Copyright owned by University of Sheffield).

In the Rhynie chert many spores have also been found preserved during various stages of germination. This feature was first described by Lyon (1957). The following four images are some examples of stages in  germination of Retusotriletes (see also insets above right), these are spores of Aglaophyton major.

 

Above: Spore preserved at the initial stage of germination where the trilete mark is beginning to split (scale bar = 25µm) (Copyright owned by University Münster).	Above: Spore preserved after the trilete mark has split with the embryo beginning to emerge (scale bar = 50µm) (Copyright owned by University Münster).
Above left and right: Preservation at further stages of embryo development (scale bar = 50µm) (Copyright owned by University Münster).