Wednesday, January 16, 2013

More on Bryums & Mniums

Bryums & Mniums are very similar to each other at first 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

Sunday, January 13, 2013

Mniums, Bryums & other wide-leaved ground mosses

There are a group of mosses that grow on the ground in especially shady places...they have wide leaves which have short to long teeth.
below is a field key to some of our common wide-leaved mosses:

and if you have a dissecting and/or compound microscope, here are some of the microscopic features:

over the next few posts, i'll go into a little more detail some of the species...such as the differences between Mniums & Bryums..and how the Mnium family is split into three distinct groups: Rhizomnium, Plagiomnium and Mnium.

Saturday, January 5, 2013

Asexual Reproduction/Vegetative Propagation

 Mosses & Liverworts can reproduce by other means than spores. The asexual strategy is much faster and less costly than sexual reproduction and can enable bryos to colonize an area quickly which becomes very important in unstable environments.

There are three basic methods bryos use in vegetative propagation: Fragmentation, Gemmae & Propagules.

Fragmentation is exactly what it sounds of the plant, usually pieces of or whole leaves, break off and form new plants. Some species have taken this further and developed 'break zones' in their leaves which makes them extremely fragile and with the lightest touch, will break off. These fragments, on finding a suitable substrate, will then develop into protonema (that thread-like stage that looks like aglae) which then develops into the leafy shoots. Two examples are Dicranum viride and Haplohymenium triste:

Dicranum viride (note all the broken leaf tips)

One shoot of D. viride showing leaf tips

Dicranum viride leaf

Haplohymenium triste leaf showing 'break zone'
The production of Gemmae and Propagules take this a step further. Now the plant is putting slightly more energy into the production of structures specifically designed to grow either into protonema or directly into a leafy shoot. 
     Gemmae are structures, one to many celled, that are basically undifferentiated...they have no growing tip and will form protonema before growing into a plant. Many bryophytes have gemmae...the liverworts are especially fond of them. they can be one-celled round structures, 2-celled ovals, multicellular worm-like things, or stellate and they're often colored orange or red (especially in the Lophozias).

Blaisia pusilla, which grows in a very unstable habitat of open, moist soil..along ditches, etc, has two different gemmae. It produces scale-like gemmae on the ends of the thallus lobes shown below:

Blasia pusilla showing scale-like gemmae on thallus lobes

It also produces these crazy flask-like structures which house ovoid, several celled gemmae which are extruded through the mouth of the flask.

Blaisia pusilla flasks

Tortula papillosa, has multicellular globose gemmae which are found right on the leaf surface:

This beautiful photo by Michael Luth, shows the gemmae on Tortula papillosa's leaves

A view of the leaf showing the globular gemmae clustered along the costa
Propagules are even further developed than gemmae, have a growing tip, and often can resemble small buds or miniature leafy shoots. these propagules can grow directly into a plant without going through the protonema stage.

Dicranum flagellare showing upright propagules which are very easily dislodged

Dicranum flagellare propagule -
note how it looks like a tiny plant with reduced leaves.

Many times the existence of gemmae or brood bodies is very helpful in determining a species. For example, Pseudotaxiphyllum elegans and P. distichaceum look very similar in the field...but if you looked at their propagules, they are easily identified:

Pseudotaxiphyllum distichaceum propagule
Pseudotaxiphyllum elegans propagule
So, whether by fragmentation, gemmae or propagules, mosses & liverworts have found an ideal way to reproduce successfully without going through the costly and iffy process of sexual reproduction.