Cytotaxonomic Studies of Some American Species of Dryopteris

Abstract

The genus Dryopteris in America is well known for the difficulties which it presents to the systematist; several of its taxa are classified differently by different authors and hybridization between species is common. Spore morphology in Dryopteris has been shown by Crane (1953, 1955, 1956) to be a most useful taxonomic character in helping to separate some of the species. For the past few years I have been engaged in cytological studies and experimental hybridization within the genus, involving both European and American material, in order to study the evolutionary processes and attempt to elucidate some of the taxonomic problems. The knowledge gained from an investigation of the Dryopteris spinulosa complex in Europe has already been published (Walker, 1955) ; stated briefly, this shows that in Europe there are three allotetraploid species, cristata (L.) A. Gray, spinulosa (0. F. Muell) Watt and dilatata (Hoffm.) A. Gray, together with two diploid forms of D. dilatata, one found in Britain and on the continent of Europe, the other in Madeira. These two diploids are very different in their division of the blades and in spore size, but studies of meiosis in experimental hybrids indicate that they are descendants of the same ancestral diploid, that which is common and part parental to both spinulosa and dilatata. A detailed report on the results obtained from a study of North American material of Dryopteris is in preparation for publication elsewhere, but perhaps the following will be of general interest to readers who have met with the taxonomic problems in this genus. Cytological investigation of cristata and spinulosa (typical) from the eastern United States shows that