Palaeoecology and palaeophytogeography of the rhynie chert plants: evidence from integrated analysis of in situ and dispersed spores.

The Rhynie cherts yield exceptionally preserved early land plants, and provide a unique insight into the nature of Lower Devonian vegetation. Hitherto they have been poorly age constrained, and the palaeoecology and palaeophytogeography of the flora are poorly understood. Well-preserved dispersed-spore assemblages have been recovered from a number of borehole cores through the stratigraphical sequence of the Rhynie outlier. They are all similar and belong with the polygonalis-emsiensis (PE) spore zone, indicating an Early Devonian age (Early (but not earliest) Pragian to earliest Emsian). Comparisons with PE spore-zone assemblages from elsewhere suggest that the flora of the Rhynie drainage basin was slightly impoverished, with certain plant taxa that occurred at other locations not represented. This probably reflects differences between the flora of an inland intermontaine basin (Rhynie) and that of the lowland flood-plains. In situ spores have been characterized for all seven Rhynie chert plants. Analysis of the distribution of these spore types in the Rhynie sequence, in addition to those of coeval deposits from elsewhere, enables interpretation of the palaeoecology and palaeophytogeography of the Rhynie chert plants. It is concluded that at least some of the plants were not highly specialized or adapted to the peculiar hot-springs environment in which they are preserved. Rather, they were components of a diverse and widespread flora, but were the only elements able to tolerate the inhospitable hot-springs environment (i.e. they were preadapted).