The cytology and distribution, together with some morphological notes and a key, are given for nine species ofDryopteris(wood ferns) in Ontario. The cytological determinations were made on 239 plants of nine species, considered as five diploid species (x = 41) (D. marginalis, D. fragrans, D. goldiana, D. dilatata, andD. intermedia), three tetraploids (n = 82) (D. spinulosa, D. cristata, andD. filix-mas), and one hexaploid (n = 123) (D. clintoniana).