HISTORICAL REVIEW OF THE UNCERTAIN TAXONOMIC STATUS OF CYSTOPTERIS DICKIEANA R.SIM (DICKIE'S BLADDER FERN)

Abstract

Cystopteris dickieana R.Sim is a rare fern protected in Britain under the 1981 Wildlife and Countryside Act. Most current floras treat it as a distinct species but ever since it was first discovered in Scotland in the 1830s, there has been considerable debate about its taxonomic status within the C. fragilis complex. This debate centres on the relative importance of two characters, the architecture of the fronds and the surface sculpturing of the spores, in delimiting C. dickieana from other taxa in the C. fragilis complex. The type specimens of C. dickieana have distinctive fronds. Plants with similar frond architecture have, to date, been recorded growing naturally only at the site in Scotland from which the type specimens were collected and at one other site nearby. The type specimens of C. dickieana also have mature spores with surface sculpturing often described as ‘rugose’. These are distinctive and unusual in the genus Cystopteris, in which most taxa have ‘echinate’ spores. However, rugose-spored plants have been recorded not only at, and near, the type locality in Scotland but also at many other sites in the northern hemisphere in populations of plants defined largely on the basis of frond architecture as C. fragilis or C. baenitzii. This indicates that spore sculpturing should not be used alone to delimit C. dickieana from other taxa within the C. fragilis complex but, despite this, the literature on ‘C. dickieana’ contains many reports of studies on material identified as C. dickieana solely on the basis of spore sculpturing. This, combined with the fact that most comparative studies have also failed to include material known to have come from the type locality, has resulted in considerable and continuing uncertainty over the taxonomic status and distribution of C. dickieana.