Bracken, (Pteridium) plants are so numerous in the British Isles that the genus is a recognised agricultural problem, subject to control methods including spraying of pteridocidal chemicals from helicopters. Plants that differ from the common weedy form (Pteridium aquilinum subsp. aquilinum) have recently been recognised, and given new species (P. pinetorum) or subspecies status. The rarity of these plants poses a conservation dilemma if weed control programmes continue in ignorance of their existence, but only if they can be shown to constitute entities distinct from the common taxon. Our aim was to address concerns that these rare and local forms may represent either environmentally-induced variation of the common taxon , or single individuals of unusual morphology. Our techniques include transplantation of rhizomes into common-garden cultivation, morphological and isozymic analyses and probing restriction digested DNA with an Adiantum chloroplast DNA clone bank. Our results to date indicate that for some of the recently proposed taxa (e.g. Pteridium aquilinum subsp. atlanticum), the data do not support the contention that any plants now growing at the type locality are distinct from the common form. The unusual form reported for plants therein may represent environmentally-induced variation of the common taxon. For other taxa our data would be consistent with recognising populations, and not merely individuals, of plants which do maintain their appearance in common garden cultivation. It would be premature to support or reject the erection of separate taxa at a particular level for the plants of these populations but the implications for bracken control programmes in areas supporting these populations will be discussed.

Key words: Bracken, fern, Pteridium