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Rhizomnium nudum (Britt. & Williams) T. Kop.

Naked Mnium

Mniaceae

General Description: This moss forms loose, dark green tufts. Stems are erect, unbranched, reddish-brown and lack rhizoids. The leaves are 4-9 x 3-7 mm in size, entire, glossy, and nearly round. They shrivel or contort very little when dry. The midrib is often red, tapering from a broad base, and usually ending below the leaf apex. Dioicous, the male plants usually have few or no leaves on the lower part of the stem, but do have large leaves that act as splash cups surrounding the terminal, disk-like heads. Fertile female plants bear a single stalk 1-2.5 cm long with an ovoid, nodding or inclined capsule.

Illustration.

Field Identification Tips: This moss can be recognized by its naked stems, particularly noticeable in male plants. This is a result of having the lower stem leaves reduced to scales and the uppermost leaves abruptly enlarged and crowded, surrounding the terminal perigonia. This gives male plants the appearance of a small green flower. The leaves of this moss are pretty distinctive, being relatively large, shiny, rounded to elliptic, rounded at the apex, and scarcely altered upon drying.

Similar Species: Species of Mnium and Plagiomnium have toothed leaves versus the entire leaves of R. nudum. The absence of rhizoids on the stem separates it from R. magnifolium. Like R. nudum, the stems of R. glabrescens also lack rhizoids, but the latter species has leaves oblong-ovate or elliptic in shape, as opposed to the obovate to nearly round leaves of R. nudum. Furthermore, the leaf borders of R. glabrescens are thickened, while those of R. nudum may be thickened near the leaf base, but not at the apex.

Habitat: On damp forest soil, humus, and along creek beds. In some parts of its range it also occurs among boulders or talus at cliff bases.

Global Distribution: In North America, it is found in the Pacific Northwest from Alaska to northern California, with inland populations in northeastern Oregon, northern Idaho, northwestern Montana, and Alberta. It also occurs in Japan and the Russian Far East.

Idaho Distribution: There is a historical collection from along the North Fork Coeur d'Alene River, Kootenai County. It is also known from a small number of collections in the Lochsa River area in northern Idaho County.

References:

Koponen, T. 1971. A report on Rhizomnium (Mniaceae) in Japan. Journal of the Hattori Botanical Laboratory 34: 365-390.

Koponen, T. 1973. Rhizomnium (Mniaceae) in North America. Annales Botanici Fennici 10: 1-26.

Lawton, E. 1964. The structure and distribution of Mnium nudum. The Bryologist 67: 44-47.

Lawton, E. 1971. Moss flora of the Pacific Northwest. The Hattori Botanical Laboratory, Nichinan, Miyazaki, Japan. 362 pp., plus plates.