A New Hymenophyllum Species in the Appalachians Represented by Independent Gametophyte Colonies

In the United States, four genera of ferns are known to exist as independent gametophyte populations (Farrar, 1967). They are able to persist, in isolation from sporophytes of the species, by vegetative reproduction, including the production of gemmae. Their apparent inability to produce normal sporophytes has led to considerable difficulty in species identification. The earliest vouchered collection of Hymenophyllum gametophytes in the southern Appalachian Mountains is one by Mary Taylor. She described the plants as growing "not far from one of the stations for Hymenophyllum tunbrigense." The widespread occurrence of independent Hymenophyllum gametophytes in North and South Carolina was first reported by Farrar (1967). He, at that time, presumed the gametophytes (Figs. 1-6) to be "the same species as the sporophyte Hymenophyllum tunbrigense (L.) J. Sm. which grows in South Carolina." Subsequent publications either supported this possibility (Farrar, 1985) or remained uncommitted regarding their identity (Wagner et al., 1970). However, the rarity (Wagner et al., 1970) and relative sterility (Farrar, 1971) of H. tunbrigense sporophytes in the Appalachians, has always been difficult to reconcile with the frequent occurrence of independent gametophytes. Furthermore, Taylor described the gametophytes in her collection as "decidedly different from the prothallia that I think are those of H. tunbrigense" (pers. comm. to W. R. Maxon, 13 Oct., 1936). There are several problems in determining whether these gametophytes are H. tunbrigense or not. Most studies of Hymenophyllum gametophytes (Atkinson, 1960; Goebel, 1888; 1905; Holloway, 1930; Stokey, 1940; 1948; Stone, 1965), have concentrated on development rather than on distinguishing features of the mature prothalli. Few studies have specifically described characters of H. tunbrigense gametophytes, and those that we have been able to find included no helpful figures (e.g. Janczewski & Rostafinski, 1875; Richards & Evans, 1972). Also, Farrar (1971) was unable to grow H. tunbrigense gametophytes in culture, and therefore did not obtain experimental data regarding gametophyte form and growth requirements and responses that would have been useful in this study. The discovery of a single juvenile sporophyte of a second Hymenophyllum species in the United States (Wagner et al., 1970) further calls into question the