Asplenium rutamuraria L. and A. septentrionale (L.) Hoffm. are two very distinct and well-defined species of ferns, generally distributed throughout Europe, and also possessing wide but interrupted ranges around the northern hemisphere. Previous to this communication, all the chromosome counts in these two species known to me, whether from Europe1,2 or elsewhere3,4, have indicated that both are exclusively tetraploid, with n = 72 chromosomes.