The Mnium Group

Mniums used to be all lumped together in one genus - Mnium...
then in 1968 T.J. Koponen separated them into different groups:

1) Leaf margin entire (or obscurely toothed): Pseudobryum, Cyrtomnium & Rhizomnium

2) Leaf margins with single teeth: Plagiomnium

3) Leaf margins with double teeth: Mnium

Let's take a look at the first group:

Rhizomniums are fairly common in our area, especially R. punctatum and R. appalachianum
Both species have leaves that have a strong border of long cells with interior cells that are roundish.
R. punctatum is much smaller than R. appalachianum and i find it most often on rocks in wet areas whereas R. appalachianum grows in wet, swampy soil.

Rhizomnium punctatum

R. punctatum - note the smooth stems

Rhizomnium punctatum also has no tomentum or brownish hairs growing up the stem; only at the base.

a nice clump of Rhizomnium appalachianum

a scan of R. appalachianum. notice how the stem is covered with brown 'stuff' covering the stem.

Pseudobryum cinclidiodes is very much like Rhizomnium appalachianum. It is similar size-wise (a BIG moss) as well as liking the same type of wet places in the woods. It's leaves are a little more oblong, and if you look really closely it actually has really short, blunt teeth. Also, the leaf border is much weaker. If you look at it under the microscope, its cells are much more elongated and are in rows that angle away from the costa. The first time i saw this, i just couldn't figure it out...it was a mnium with bryum cells!

Pseudobryum cinclidiodes, compare the leaf shape to R. appalachianum

The last moss of this group is Cyrtomnium hymenophylloides...a rare moss of northern areas growing on limy ledges.  it's quite small, a beautiful blue green with round leaves basically in two rows.

Cyrtomnium hymenophylloides