Mosses of Central Florida 29. Plagiomnium cuspidatum

Plagiomnium cuspidatum

The upright stems with broad ovate leaves and nodding
capsules of Plagiomnium cuspidatum suggest a species
of the Bryaceae until one takes a closer look.
Photo by Robert A. Klips, Ohio Moss and Lichen
Association

(Hedwig) T. J. Koponen (Mniaceae)forms mats on moist soil, on rotting logs, or at the bases of trees in moist habitats, and has two forms of leafy stems; creeping sterile stems, and upright fertile stems.  Our local material appears to be all sterile, however.

The most distinctive characteristic of this species is its ovate to diamond-shaped leaf with a prominent midrib and conspicuous, narrow, sharp teeth in the upper half.  The leaf base is broad and clasps the stem.  The leaf cells are roundish, with thick, translucent walls. The leaves are twisted when dry.  The nodding, cylindrical to ovate capsules arise on elongate stalks from erect leafy stems.

The leaf of Plagiomnium cuspidatum  resembles that of a Bryum, 
but with many long, narrow teeth along the edge in the upper half.
Photo courtesy the Western New Mexico University
Department of Natural Sciences and the Dale A. Zimmerman
Herbarium,, Plants of the Gila Wilderness.

The nodding capsules are a plump, ovate-
cylindrric. Photo by Robert A. Klips, Ohio 
Moss and Lichen Association

This species, often filed under the older name of Mnium cuspidatum, is widespread in North America, even reaching Alaska and Greenland, and in Florida it is found from the panhandle to Miami-Dade County. Two other species are found in the state: P. ciliare only in the panhandle, and P. floridanum throughout the northern half of the state.  In P. ciliare the marginal teeth typically extend down toward the base, rather than just the upper half, and these are usually blunt.  P. floridium is nearly  indistinguishable, but the leaves more elliptical and with less flaring leaf bases.

The prominent, narrow teeth arise from a thickened border of rigid cells.  To the inside, cells are small, rounded, and thick-walled.  Photo from Wikimedia Commons,  licensed by Creative Commons..

This upright, fertile stems of this species might also be confused with members of the Bryaceae, such as Bryum argenteum, or Rosulabryum capillare, which also have broad leaves with a strong costa and nodding capsules, but their leaves do not have prominent teeth and their cells are much larger and more elongate.
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