Fissidens appalachensis R.H. Zander

Distribution

Endemic to eastern U.S.A. North Carolina, Pennsylvania, South Carolina, Tennessee.

Habitat

Aquatic in mountain streams, ranging from 1200 – 5600 ft elevation, tightly attached to crevices of submerged rocks in swiftly flowing water. Also aquatic or semi-aquatic attached to rocks (usually the lower edges near the stream bottom) in slow moving, shallow water of headwater streams and mountain springs/seeps. More rarely growing just above the water’s surface attached to a thin layer of sandy sediment atop low-lying rocks or stones in quiet streams. Plants may be covered by a foot or more of running water, in which case collecting specimens for documentation may require blindly picking moss bits from underwater or pulling smaller rocks above the water’s surface for inspection. In total submergence of swiftly flowing water F. appalachensis is more commonly found on the downstream nose of rocks especially in crevices of the undercut rock surface where presumably there is calmer water surrounded by eddies and turbulent flow.

In the upper Santeetlah Creek drainage near the headwaters of Johns Branch, robust F. appalachensis occurred on the upper surface of wet rocks (stones) that had accumulated a thin sandy layer of sediment in which the plants were attached. The sediment layer was surely the result of periodic submersion during high rainfall. Here material was collected by cutting the sandy sediment layer away from the solid rock underneath (see specimens Davison & Hicks 2970 and Davison 4003, the later specimen with abundant sporophytes; neither specimen was submerged at the time of collecting).

Brief Description and Tips for Identification

Plants green, becoming blackish below. Stems 5-15 mm long. Leaves in 5-22 pairs. Leaves limbate (with a differentiated border of elongate cells), the limbidium (border) extending to leaf apex or ending a few cells below. The limbidium of 2-5 layers of cells as seen in cross section. Description from Crum and Anderson (1981) and Pursell (2007).

Monoicous. Rhizautoicous or synoicous (Pursell 2007). The only published account of reproductive ecology is Smith (1984): “Well-developed sterile shoots form compact tufts isolated in cracks of rocks or in linear seams along rock fissures in the submerged zone. Fertile shoots occur frequently in the zones above or at the mean water-flow level. Sporophytes mature and spores are liberated from late July through September.”

The genus Fissidens is easily recognizable by its leaves. Unlike most other mosses the leaves are inserted in two rows, one on each side of the stem. Each leaf has a “pocket” or “slot” formed by portion of the leave blade that is split into what is called the vaginant lamina (one lamina lies atop the other with a small space between thus forming a sheath). Beever et al. (2002) explained other specialized terms used to describe the leaf morphology.

Anderson and Zander (1973) listed sixteen species of Fissidens occurring in the southern Blue Ridge Province of which only F. fontanus is truly aquatic. Fissidens appalachensis is typically fully submerged but may be found just above, or at the water’s surface. Regionally, F. appalachensis is distinguished from all other congeners (except F. bryoides) by a limbdium (a leaf border formed of elongate cells) that reaches the leaf apex.

F. appalachensis is potentially confused with forms of F. bryoides, especially F. bryoides var. pusillus that may co-occur with F. appalachensis on wet, streamside rocks. F. bryoides (var. pusillus) is so similar that Richard Zander in the publication naming F. appalachensis included a specimen as F. appalachensis that the late Ron Pursell (Fissidens monographer) reidentified as F. bryoides (see Pursell and Allen 1996). Distinctions setting F. appalachensis apart from F. bryoides var. pusillus include “usually larger plants, longer and comparatively narrower leaves, stronger limbidia, percurrent costae, and infrequently bistratose laminal cells” (Pursell and Allen 1996). In addition, Pursell and Allen (1996) emphasized a habitat distinction: F. bryoides grows on “surfaces of wet stones and rocks near the edges of streams” where submergence would occur only “for a time” during “periods of the year” (presumably during high rainfall). F. appalachensis grows “submerged in crevices among rocks in rapidly running streams” or partially exposed above water on the sides of emergent rocks.

Sérgio, C., & Pursell, R. A. (2001) included F. appalachensis in a complex of aquatic Fissidens that includes the very similar F. jansenii Sérgio & Pursell (Portugal), F. rivularis Schimp. (Europe), and F. geppii Fleisch. (Asia).

Salient Features

• Aquatic habitat
• Leaf margin with a band of differentiated cells forming a limbidium (border)
• Limbidium strong
• Leaves narrow (a relative concept, see images below comparing to F. bryoides)

References

Anderson, L. E., & Zander, R. H. 1973. The mosses of the southern Blue Ridge Province and their phytogeographic relationships. Journal of the Elisha Mitchell Scientific Society, 15-60.

Beever, J., Malcolm, B., & Malcolm, N. 2002. The Moss Genus Fissidens in New Zealand: Te Puninga Fissidens i Aotearoa: an Illustrated Key. Micro-Optics.

Bruggeman-Nannenga, M. A. 1978. Notes on Fissidens. I and II. I. On the arbitrary nature of the division in section of the genus Fissidens. II. Remarks on some species of the Fissidens bryoides complex. Proceedings Koninklijke Nederlandse Akademie van Wetenschappen. Series C, Biological and Medical Sciences 81: 38 7-402.

Crum, H. A., and L. E. Anderson. 1981. Mosses of Eastern North America (Vol. 1). Columbia University Press.

Pursell, R. A. 2007. 21. Fissidentaceae Schimper. Flora of North America, 27, 331-357.

Pursell, R. A., & Allen, B. 1996. A comparison of Fissidens appalachensis and F. bryoides var. pusillus. The Bryologist, 75-80.

Sérgio, C., & Pursell, R. A. 2001. Fissidens jansenii (Fissidentaceae; Bryopsida), a new aquatic species from Portugal. The Bryologist, 104, 378-381.

Smith, D. K. 1984. New characters and revised distribution of Fissidens appalachensis Zand. The Bryologist, 87, 259-260.

Zander, R. H. 1969. A new species of Fissidens from the Southern Appalachian Mountains. The Bryologist, 406-409.