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Mosses: A Closer Look

By Dr. Bill Buck

Mosses are small green plants that most of us see, but don't really look at. Typically, we are more familiar with the word than with the plants themselves, and often confuse them with lichens. Most of the biological world that we see (including ourselves), have two sets of chromosomes. The only part of the life cycle that has a single set of chromosomes is typically short-lived and reduced (e.g., pollen, sperm). Mosses, on the other hand, are just the opposite.

The green, leafy plants have but a single set of chromosomes. Only after formation of sex organs (antheridia (male) and archegonia (female)), and then fertilization, do we get the relatively short-lived part of the life cycle with two sets of chromosomes. These stalked capsules are dependent on the green leafy plants and each contains hundreds of thousands of spores.  Each of the spores, once again, only has a single set of chromosomes and is typically wind dispersed.  

Mosses may be distinguished from lichens because mosses always have leaves but lichens never do. Lichens are a complex organism, composed of both a fungal and an algal component. The fungus (which carries the name of the lichen itself) protects the algal cells and reproduces. The algae are usually sandwiched between two fungal layers and are thus protected from extremes of the environment, and provide photosynthetically produced nutrition for the fungus.

Mosses are well adapted to a fluctuating wetting and drying cycle. Most moss leaves are only a single cell thick and thus dry out and rehydrate quite rapidly. There is even research underway to try and take the genetic basis of this ability and transfer it to crop plants.

Although mosses occur in almost every habitat except marine ones, they are most abundant and speciose in more humid habitats. It is exactly this tendency which explains why mosses are said to be found on the north side of trees. In habitats that are only slightly moist, it may well be that most of  the mosses are on the north (i.e., shaded) side of the tree. However, if there is more moisture, as there usually is locally, then mosses will grow on any side of the tree, as well as on rocks and soil.

Some mosses have a very short life cycle, and go from spore to spore in only a month or two, typically in the spring or fall when the trees do not have leaves, and thus are not competing for light. These are typically very small plants, growing on bare soil and often with their capsules on very sort stalks, resulting in the capsules being immersed among the leaves rather than elevated above them.

The size of moss plants ranges from about 1 mm tall, to several meters. In our area, most mosses fall between these two extremes. Each dense cushion of moss that you might see in the woods, may contain many hundreds or even thousands of individual plants. Mosses play diverse, but subtle, roles in the environment. They help bind soil and prevent erosion; they serve as a seedbed to vascular plants; and they help maintain the moisture level in the habitat by absorbing water and then releasing it slowly. Mosses also host a large number of invertebrates, which mostly do not eat the plants, but use them for shelter.

As part of our natural resource inventories of our preserves, mosses are being included in our findings. However, so far, only Field Farmstead Preserve has been surveyed for mosses. The collections were mostly made on a single afternoon, so certainly the list below is not complete. Nevertheless, 47 moss species have been recorded. Here is a list of names. Unlike many more prominent, we might even say charismatic, organisms, most mosses do not have common names. Nevertheless, everyone knows some scientific Latin names, and should not be intimidated by them. For example, we all know Chrysanthemum, Gladiolus and Cosmos, and many of our common names are only minor modifications of Latin names, such as rose (Rosa), pine (Pinus) and poplar (Populus). So, don't let the Latin names discourage you from learning about these green jewels.

Some Common Mosses found in our area:

Anomodon attenuatus
Atrichum angustatum
Atrichum crispum
Atrichum oerstedianum
Barbula unguiculata
Brachythecium plumosum
Brachythecium populeum
Brachythecium rivulare
Brachythecium rutabulum
Brachythecium salebrosum
Bryhnia novae-angoliae
Bryoandersonia illecebra
Bryum argenteum
Callicladium haldanianum
Climacium americanum
Dicranella heteromalla
Ditrichum pusillum
Entodon cladorrhizans
Entodon seductrix
Eurhynchium hians
Forsstroemia trichomitria
Grimmia pilifera
Haplocladium virginianum Hedwigia ciliata
Hygroamblystegium tenax
Hypnum imponens
Hypnum lindbergii
Hypnum pallescens
Leska gracilescens
Leucobryum glaucum
Orthodicranum fulvum
Orthodicranum montanum
Orthotrichum stellatum
Plagiomnium cuspidatum
Plagiothecium cavifolium
Plagiothecium laetum
Platygyrium repens
Pleuridium subulatum
Polytrichastrum ohoiense
Polytrichum commun
Pylaisia polyantha
Pylaisia selwynii
Pylaisiadelpha tenuirostris
Schistidium confertum
Schwetschkeopsis fabronia
Thuidium delicatulum
Ulota hutchinsiae