Evidence for the Origin of the Hybrid Cliff Fern, Woodsia x Abbeae (Aspleniaceae: Athyrioideae)

Abstract

After its original description as Woodsia oregana (cathcartiana) x W. ilvensis, W. x abbeae has been interpreted by all authors as the hybrid between W. ilvensis and W. scopulina, on the basis of its scopulina-like hairs, which are absent in W. ilvensis and W. oregana. Evidence is presented here that the form of the pinnae, glands, indusial segments and sorus, and the chromosome number, support the original interpretation of W. ilvensis x oregana. Woodsia x abbeae Butters, a hybrid cliff fern, is found on cliffs and talus slopes in the region of the northern Great Lakes. Although one par- ent is clearly W. ilvensis (L.) R. Br., a problem exists with regard to the identification of its other parent. The description by Butters (1941) as the hybrid W. cathcartiana Robinson x W. ilvensis, was based on plants collected by L. B. and E. C. Abbe, on the north side of Pigeon Bay, Thunder Bay District, Ontario, Canada. In his account, Butters described characters of W. ilvensis and W. cathcartiana to be found in the hybrid, and stated that in none of the hybrid plants is there any suggestion of W. scopulina D. Eaton. All three species occur in the Thun- der Bay area and in northeastern Minnesota where the hybrid had been found. Woodsia cathcartiana was considered by Brown