Thursday, December 23, 2010


It's time again for the next installment of my series: Better Know Your Mosses!

Part 5 will be a continuation of my previous episode: How do mosses survive? Here you will learn just how different mosses really do look from each other

Growth Form

You can divide all mosses into two growth forms. They can be either acrocarpous or pleurocarpous. The singular characteristic that sets them apart is the location of the sporophyte. If it is growing terminally on the gametophyte (i.e. coming out of the top) it is an acrocarp. If it is growing out of the side of the stem it is a pleurocarp. Generally you can tell which one a moss fits into without needing to find the sporophyte by observing its habit - and I don't mean watching it bite its nails or whistling... A plant's habit refers to its morphological appearance. It could mean tree habit or an herbaceous habit. Acrocarps in mosses are generally upright and pleurocarps are generally prostrate.

Dicranella heteromalla: acrocarp

Thuidium delicatulum: pleurocarp

Life Form

Even within the 2 catagories of acrocarp and pleurocarp, mosses can look vastly different. So they have been sub-categorized into different life forms:

Dendroid: Rhodobryum roseum

Weft: Hylocomium splendens

Mat: Hypnum imponens

Turf: Polytrichum commune

Cushion: Leucobryum glaucum

There are more forms mosses can take, but these are at least most prevalent you will come across on your daily (I hope) outdoor excursions. One thing I am especially fascinated by these life forms is where they can be found. It all has to do with water. If you were to plot the frequency of these forms (from dendroid to cushion as listed above) against regions ranging from mesic (wet) to xeric (dry) conditions, you would conclude that these life forms are indeed a function of water availability.

You can see difference in morphology in areas ranging from mesic to xeric based on the nature and capacity of capillary channels within each life form to conduct water.

It makes sense if you think simply. You will find cushion forms in drier, upland areas because that form makes a dense colony, the denser the colony, the more water it can hold onto within its capillary spaces. Mosses found in saturated areas will be more "fern-like" and not as compact because of the abundance of water, they don't have to worry about loosing it. Get it?

the plasticity of moss morphology is simply amazing. You can easily judge the typical conditions of a site based on the form moss takes. Here's a real-world application: Say you are house hunting. Your Realtor takes you to see this beautiful old home. You scan around the foundation outside and notice a plethora of pleurocarpus moss colonizing the base of the home along with many little cracks in the foundation. What does that mean? It means you would potentially be the owner of a beautiful mossy home with terrible water and mold problems in your foundation!

Next time you see a little moss, read about its life in its forms; let it tell you its story and the story of its surroundings.