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

The remarkably preserved Rhynie chert plants remain pivotal to our understanding of early land plants. The extraordinary anatomical detail they preserve is a consequence of exceptional preservation, by silicification, in the hot-springs environment they inhabited. However, this has prompted questions as to just how typical of early land plants the Rhynie chert plants really are. Some have suggested that they were highly adapted to the unusual hot-springs environment and are unrepresentative of 'normal' plants of the regional flora. New quantitative analysis of dispersed spore assemblages from the stratigraphical sequence of the Rhynie outlier, coupled with characterization of the in situ spores of the Rhynie chert plants, permits investigation of their palaeoecology and palaeophytogeography. It is shown that the Rhynie inland intermontane basin harboured a relatively diverse flora with only a small proportion of these plants actually inhabiting the hot-springs environment. However, the flora of the Rhynie basin differed from coeval lowland floodplain deposits on the same continent, as it was less diverse, lacked some important spore groups and contained some unique elements. At least some of the Rhynie plants (e.g. Horneophyton lignieri) existed outside the hot-springs environment, inhabiting the wider basin, and were indeed palaeogeographically widespread. They probably existed in the hot-springs environment because they were preadapted to this unstable and harsh setting.This article is part of a discussion meeting issue 'The Rhynie cherts: our earliest terrestrial ecosystem revisited'.