The presence of verrucate spores (as opposed to the normal spiny spores) has been used to circumscribe Cystopteris dickieana . Although genetic analyses have not been undertaken, we think the verrucate spore is probably a recessive feature controlled by one or a few genes. While present at low frequency in much of the range of C . fragilis , verrucate spores are particularly prominent in the Great Plains. Perhaps in this region the genetic combinations specifying verrucate spores have been fixed. Following R. F. Blasdell (1963), C . dickieana is also considered here to be conspecific with C . fragilis because (1) early stages in the development of spiny spores can appear verrucate (A. C. Jermy and L. Harper 1971), (2) the hexaploid cytotypes discussed above always have verrucate spores, regardless of their parentage, (3) individuals with verrucate spores can be found in populations that are otherwise uniformly spiny-spored, and (4) individuals and populations that have verrucate spores are not otherwise (morphologically, ecologically, or genetically) distinct from those that have spiny spores.
Especially in the western portion of its North American range (British Columbia, Washington, Montana, Idaho, Oregon, California), Cystopteris fragilis appears to be developing morphologically and ecologically distinctive variants. Hybrid individuals with aborted spores have been discovered, and plants from these areas increasingly tend to grow on both soil and rock and to have slightly different morphologies on the two substrates. These variants intergrade, however, and are not sufficiently distinct to warrant species status. This polymorphic polyploid is probably actively speciating at the tetraploid level, perhaps through gene silencing (C. R. Werth and M. D. Windham 1991).
Cystopteris dickieana, commonly known as Dickie's bladder-fern, is a fern with a wide distribution in the Northern Hemisphere. There is debate amongst botanists as to whether it is a species in its own right or a variant of C. fragilis.
C. dickieana is native to Canada and the United States, a variety of European countries including Russia and also north Africa and the Andes. It is typically found in montane habitats below the tree-line, although it is also grows at lower altitudes in locations with cool summers.[1]
The first recorded discovery of the plant was made by William Knight, Professor of Natural Philosophy at Marischal College, Aberdeen in Scotland. Knight came across a small population growing on base-rich rocks in a sea cave (known locally as a "yawn") on the coast of Kincardineshire. The first publication to record it was the 1838 Flora Aberdonenis which included a note of its occurrence written by a pupil of Knight's, George Dickie. Dickie also sent a live specimen to Robert Sim, a nurseryman from Kent, who believed it to be a new species and published his views in the 1848 edition of the Gardener's and Farmer's Journal, naming it C. dickieana.[1]
Rarer British ferns came under severe threat from Victorian fern collectors in the mid 19th century in Scotland, a period of collecting that became known as Pteridomania (or "fern-fever"). In 1860 Dickie reported that the original colony had been extirpated from the yawn where its original discovery had occurred. The evidence for this is conflicting, but today there is a population of more than 100 plants there, where it grows in a roof fissure in the company of Athyrium filix-femina and Dryopteris dilatata.[1][2][3]
Taxonomic classification within the genus Cystopteris is complex. Within a year of Sim's publication Thomas Moore stated his view was that, on balance, Dickie's Bladder-fern was a variety of C. fragilis. Various opinions have been published over the intervening years, with a consensus that C. dickeana was a separate species emerging in the 1930s, although recent research suggests that Moore's caution may have been appropriate.[1][4] C. dickeana has broader, less divided and more closely spaced pinnae than C. fragilis and the spores of the former are typically wrinkled and ridged rather than the spiny form of the latter's. However, there are significant variations within the populations of both forms and these characteristics are by no means fixed. On the other hand, there is also evidence that crosses of the two types produce sterile hybrids.[1] C. Xmontserratii (Prada & Salvo) Fraser-Jenkins is a proposed hybrid between C. dickeana and C. fragilis.
The treatment of Cystopteris in the Flora of North America (1993) regards Cystopteris dickieana as a synonym of Cystopteris fragilis.
In the UK the fern's natural population is entirely confined to Scotland, where it is protected under the Wildlife and Countryside Act 1981.[5]
Lusby, Phillip and Wright, Jenny (2002) Scottish Wild Plants: Their History, Ecology and Conservation. Edinburgh. Mercat. ISBN 1-84183-011-9
Cystopteris dickieana, commonly known as Dickie's bladder-fern, is a fern with a wide distribution in the Northern Hemisphere. There is debate amongst botanists as to whether it is a species in its own right or a variant of C. fragilis.
