Appalachian trichomanes, weft fern

Plants on rock, occasionally epiphytic. Sporophytes not known. Gametophytes entirely filamentous, much branched, persistent. Gemmae composed of short filaments of undifferentiated cells.

On noncalcareous rocks in deeply sheltered crevices and grottoes; 150--1800 m; Ala., Conn., Ga., Ill., Ind., Ky., Md., Mass., N.H., N.J., N.Y., N.C., Ohio, Pa., S.C., Tenn., Vt., Va., W.Va.

Throughout the eastern uplands of the United States, gametophytes of Trichomanes intricatum form feltlike populations covering up to a square meter or more of rock surface in climatically moderated rock shelters and narrow canyons. Sporophytes are not produced, and reproduction is by gemmae and by perennial gametophyte growth and branching.

Filamentous gametophytes of the various Trichomanes species have not been distinguished morphologically. Enzyme electrophoresis, however, has shown the vast majority of independent Trichomanes gametophyte populations, as well as all of those existing beyond the range of sporophytes of T . boschianum and T . petersii , to be T . intricatum . (All populations of gametophytes tested in Arkansas and several populations in the immediate vicinity of sporophytes of T . petersii and T . boschianum in eastern states have enzyme banding patterns identical to one or the other of those species.) The adaptation of T . intricatum to far northern habitats and its inability to produce sporophytes suggest that this is a distinct taxon, possibly derived from a pre-Pleistocene North American species possessing a normal alternation of generations (D. R. Farrar 1985, 1992).