Wednesday, January 16, 2013

More on Bryums & Mniums


Bryums & Mniums are very similar to each other at first glance...one usually notes that they both have capsules that are 'droopy' and they both have leaves that are bordered with long cells with shorter cells in the middle. Both are acrocarps with the capsules coming out of the tip of the plant and not on a side branch.

Let's start with the differences: although both groups have drooping capsules, Bryums have capsules with distinct 'necks':
Bryum caespiticium capsule
the neck is the top smaller 'bulge' before the stem.
Plagiomnium cuspidatum capsule (with calyptra)
note that although the capsule is drooping, there is no 'neck' to it
Bryum leaves tend to be more lanceolate, with no or few teeth and often end in a sharp needle tip:

Bryum caespiticium leaf

Mnium leaves tend to be large-ish, rounded, oblong, elliptical or obovate and often have obvious teeth (excepting the Rhizomnium group, which we'll talk about later).

Mnium spinulosum leaf

Plagiomnium ciliare leaf


Although both groups have leaves that are bordered with long cells, the border is usually quite strong in the Mniums and weaker in Bryums. The interior cells are also different, with Mnium cells being generally round or hexagonal and Bryums having long rectangular or diamond-shaped (rhomboidal) cells.

This drawing is a section from the edge of Plagiomnium ciliare,
note the rounded interior cells bordered by several rows of long cells
and the long, multicellular teeth

Interior  rhomboidal cells from Rhodobryum ontariense


So, now you know how to tell a Bryum from a Mnium...
next post we'll talk about the main groups of Mnium: Rhizomnium, Plagiomnium & Mnium


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