There are three basic methods bryos use in vegetative propagation: Fragmentation, Gemmae & Propagules.
Fragmentation is exactly what it sounds like...parts 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'|
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|