Chromosomeounts of 156 in root tip cells of a bracken plant growing in a natural British popultaion confirm the first record of a triploid in this species. Spore and stomatal measurements supporst the contention of earlier work that cell size is correlated with ploidy level in ferns, but the plant is unusual in comparison with other odd-numbered polyploids in its degree of fertility ('good' spore and functional gametophyte production). Two-dimensional mapping based on isozyme electrophoresis reveal substantial spatial dimensions for the triploid, indicating a plant of considerable antiquity.