Morphotype and conflicting taxonomies in Pteridium (Dennstaedtiaceae : Pteridophyta)

摘要

Conflicting taxonomic treatments of the diploid bracken ferns of the Laurasian lineage within Pleridium are briefly reviewed. The infraspecific entities recognised in this section of the genus can be separated on morphological, phenological and physiological criteria into two main groups referred to respectively as 'aquilinum' and 'latiusculum' morphotypes. Evidence of gene flow between morphotypes is discussed, including the finding from DNA studies that taxa of the 'aquilinum' and 'latiusculum' morphotypes in each major geographic region are more closely related to the contrasting morphotype from the same region than to the corresponding morphotype front another region. It is proposed here that the 'aquilinum' and 'latiusculum' morphotypes may be regarded as mediated by a simple genetic polymorphism involving alternative pleiotropic alleles at a single major morphogenetic locus comparable to those previously described in Athyrium and postulated in Asplenium and Pteridium, but Other possible models are discussed.It is concluded that P. aquilinum is best treated as a single species containing at present 11 subspecies.