Dryopteris in the Huron Mountain Club Area of Michigan

Abstract

The seven species of woodferns (Dryopteris) of the Huron Mountain Club area, a natural preserve in northern Michigan, are described briefly with respect to their habitats and chromosomes: (1) Shaded upland ravines (“D. dilatata,”D. intermedia, D. marginalis); (2) vertical rock cliffs (D. fragrans) ; (3) marsh and swamp (D. cristata, D. spinulosa, D. intermedia); and (4) rocky island habitat (D. filixmas, D. intermedia, andD. marginalis). Various sterile hybrids were found:D. cristata Xintermedia, D. cristata Xmarginalis, D. “dilatata” Xmarginalis, D. “dilatata” Xintermedia, D. intermedia Xmarginalis, andD. intermedia Xspinulosa. No new allopolyploid or apogamous hybrids were found. All of the crosses grow where the parents are close by, except thatD. cristata Xmarginalis occurs in marshes where the latter parent is absent. Chromosome studies yielded a number of new cytogeographical records, of which the following are of greatest interest:D. “dilatata” Xintermedia andD. “dilatata” Xmarginalis, both with ca. 82 unpaired chromosomes at meiosis;D. filixmas, with 82 pairs;D. filixmas Xmarginalis, 123 singles; andD. fragrans, 41 pairs. An attempt to identify the “Lake SuperiorDryopteris dilatata” gave negative results. It is not the same as “Western dilatata” nor is it conspecific with the easternD. campyloptera. It is now clear that two distinct taxa have been erroneously combined in the “Gray’s Manual Range.” Epidermal and indusial glands may be either present or absent in both of the eastern American taxa. Other observations on glands indicate that their presence does not necessarily mean that the plant is a hybrid withD. intermedia as one of the parents. Gland size and density vary considerably, and gland size is not necessarily correlated with sizes of other epidermal cells. As evidenced by the conditions in the Huron Mountain area we conclude that man-made disturbance is not a necessary condition for hybridization between species ofDryopteris. Crosses form naturally under the primitive conditions of forest and swamp.