Common ground between two British Pennsylvanian wetland floras: Using large, first-hand datasets to assess utility of historical museum collections

Studies on the macrofloral record of the Pennsylvanian palaeotropical peat-forming wetlands (‘coal swamps’) depend heavily on historical collections in museums. This paper examines the robustness of such collections for macrofloral studies. 110,000 individually recorded specimens from South Wales, field collected by David Davies during the early 20th century, were compared with the 6500 museum voucher specimens derived from them, eventually intended for a representative teaching collection. This showed that the voucher collections accurately reflect the order of abundances of the plant groups as documented in the field records, but not their actual numerical abundances. These Welsh data were then compared with the available museum collections for similar-aged macrofloras in the nearby Bristol–Somerset Coalfield. Cluster analyses and Detrended Correspondence Analyses were performed (1) on the raw data recorded on the museum labels, (2) on standardised data that were updated to reflect the currently accepted taxonomy for these fossils, and (3) on standardised data in which single occurrences of taxa have been removed. The results suggest that unstandardised museum collection data can reveal meaningful biostratigraphical and biogeographical patterns, but that these become clearer with the standardised data. The effect of removing the singleton taxa was less clear, although it did provide a slightly enhanced resolution with cluster analysis. Whilst previous studies have considered these to be separate basins, with the Bristol–Somerset coalfield being proximal to South Wales on the mid-Pennsylvanian Variscan Front, results show an overall consistency between the two basins and suggest a common gene pool and vegetational physiognomy as well as a general stasis through time based on relatively stable environmental and growth conditions. The study confirms that even unrevised historical collections can provide some data to help understand the dynamics of these systems. However, it also underlines the importance of taxonomy in such studies as it helps improve both the biostratigraphical and biogeographical resolution.

► Studies on Pennsylvanian coal swamp macroflora depend on museum collections.
► A collection was examined as a test case for biases and real-world utility.
► Presence/absence format, updated nomenclature, singletons removed gave best results.
► S Britain part of transitional phase from lycopsid- to marattialean-dominated swamps.