This is a very striking visual mutant that exhibits a distinct green polka dot appearance in cells of both gametophytes and homozygous sporophytes when viewed with a low power microscope. In sporophytes, older leaves of individuals homozygous for this mutation have an attractive silver-green appearance. Although there is a slight reduction in growth and a decrease in spore viability* in spores produced from homozygotes, gametophytes carrying the polka dot mutant and homozygous polka dot sporophytes grow nearly as well as the wild type. This recessive trait has been observed in several independent selections that have been generated using both X-rays and EMS as a chemical mutagen. A study of the trait, using transmission electron microscopy, was not successful in discerning the structural basis of the phenotype. The phenotype is associated with a clumping of chloroplasts and other organelles around the nucleus. It may involve some disruption of the cytoskeleton. The pleiotropic effect of reduced spore viability is associated with somewhat fragile spore walls. Different degrees or ‘strengths’ of the clumping phenotype are positively associated with increased spore wall weakness *NOTE: Because of the decreased spore viability associated with spores produced by cp/cp homozygotes, presterilized and bulk spores are supplied in larger quantities than other stocks. Although inviable spores will be apparent in cultures, the increased number of spores provided will produce adequate numbers of gametophytes.

Vaughn, K. C., L. G. Hickok, T. R. Warne and A. C. Farrow. 1990. Structural analysis and inheritance of a clumped-chloroplast mutant in the fern Ceratopteris. J. Heredity 81: 146-151