Gymnocarpium robertianum occurs in numerous localities in eastern Canada, especially in Ontario and Quebec where it is widely distributed; populations are small. Hybrids with G . robertianum are extremely rare. Gymnocarpium × heterosporum W. H. Wagner, a putative triploid hybrid between G . robertianum and G . appalachianum , is known only from one county in Pennsylvania (plants now extirpated, K. M. Pryer 1992). Gymnocarpium × achriosporum Sarvela, a putative tetraploid hybrid between G . robertianum and G . dryopteris , is known only from Sweden and two localities in Quebec. Both hybrids resemble G . robertianum in their leaf morphology and dense glandularity but have black, malformed spores.