Two groups of plants*, mosses and lichens, distinguish themselves by being able to grow, reproduce and colonize new spaces within appropriate habitats and be of the smallest stature of all other terrestrial plants throughout the Earth’s many ecosystems. In fact, in either case, being small is essential to each one’s success. They both thrive in some of the harshest conditions – extreme cold, extreme heat, very wet conditions and very dry conditions that cause long periods of inactivity that the plants simply wait out. Ideal conditions are in temperate situations in bright to shady light with ample moisture.

  The two groups, however, achieve their place in the natural world in very different physical and ecological ways. With a hand lens and a microscope, a whole world of beauty reveals the secrets of these important plants. During Winter, in temperate and boreal ecosystems, mosses and lichens are among the last to enter a period of dormancy and among the first to actively photosynthesize when conditions become favorable.

Mosses

  Mosses are best described by the typical plant features that they lack. Mosses have no roots (for the purpose of feeding the plant), no flowers, no seeds, no fruits, and no vascular system (xylem and phloem) for transporting water and nutrients. They consist of simple stems with leaves. Each moss leaf is one cell thick and very permeable to moisture and to nutrients within the moisture. The stems are held in place on a substrate (rock, soil, tree bark, dead wood) by wiry holdfast structures called rhizoids. With the simplest of physical features, mosses have evolved into 22,000 species worldwide. In Vermont, there are an estimated 424 species of mosses.

  Mosses can grow in full sun habitats, but most mosses are specially adapted to grow well in the light shade to full shade of forested habitats. They are capable of becoming completely dormant when dry and rehydrating to fully functional within 20 minutes. Mosses are masters of acquiring and holding onto moisture which is critical to all of their functions – gaining nutrients; producing sporophytes and vegetative bodies for reproduction; and growing new plants, stems and leaves. They accumulate bits of pollen, dust, dirt, plant remains and the shells of macro-invertebrates that are deposited by rain and wind. This debris builds up and forms the first soils for higher plants to establish a small foothold.

  Wildlife and humans have made extensive use of mosses, especially in northern regions. While the nutrient levels are low for most creatures, tiny insects graze on moss stems and spend their entire life in a moss forest. Many birds and mammals use moss as a soft lining to a nest or a den. Sphagnum mosses have been utilized as naturally sterile bandaging material. Indigenous people around the northern regions use mosses as cushioning material, as swaddling for infants and as insulation inside other articles of clothing.

Lichens

  Lichens have evolved from more primitive life forms than mosses that include the mutually beneficial relationship of a fungus and either an alga or a cyanobacteria. The fungal partner forms the bulk of the plant, provides a means of holding onto a substrate, and supplies protection from extreme cold and dessication. The algal or cyanobacterial partner (10% of the plant’s biomass) produces food for itself and its partner. Lichens have evolved into 14,000 species worldwide. In Vermont, 586 lichen and lichen allied species are known from Herbarium specimens and current research. It is expected that that number will increase with ongoing research in the field.

  Lichens grow in all habitats on Earth. They become dominant in the landscape above treeline on mountains and in the Arctic Tundra and Taiga regions. Lichens are cryptobiotic, meaning that they have the ability to completely shut down life processes and to quickly resume photosynthesis when conditions are right. They can photosynthesize down to minus 20 degrees C. Lichens acquire all of their basic nutrients from air, humidity, rain, snow and the substrate upon which they grow - soil, rock, tree bark. They metabolize acids in minute quantities that gradually erode the surface of the substrate and create conditions for the first mosses to gain a foothold.

  Lichens too have a low nutritional value and are not good food for wildlife. Female ruby-throated hummingbirds build their nest out of spider silk to which they apply plates of lichen to the outside as a means of waterproofing the nest. For some animals of the far north, for example, caribou and reindeer, lichens are a mainstay during the Winter months and supply the animals with the bulk they need to last until the next Summer’s supply of nutritional grasses. These members of the deer family have special bacteria in their rumen to digest lichen. Native people who take a caribou in Winter often first enjoy the partially digested lichen mass from the rumen before rendering the rest of the animal. People have used lichens for dye for clothing; they have dried and ground lichens into a flour to mix into bread; and they have stewed lichens as a thickener for soups.

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* Footnote on the Classification of Mosses and Lichens

  Mosses, along with liverworts and hornworts, are called bryophytes (Division Bryophyta) and are the most primitive members of the Kingdom Plantae.

  Lichens are generally treated as members of the Kingdom Plantae, even though the dual nature of their mutualistic existence comprising a mycobiont (a fungus) and a photobiont (an algal or cyanobacterial organism) that makes up a lichen suggests that they belong partially in the Kingdom Fungi (for the fungal partner) and in one of two other Kingdoms: Kingdom Monera (if the photobiont partner is cyanobacteria) or Kingdom Protista (if the photobiont partner is an alga). Lichens take their Genus and Family names from the mycobiont species.

- Deborah Benjamin

Recommended Reading

Forests of Lilliput, The Realm of Mosses and Lichens by John Bland. Publisher: Prentiss Hall, 1971. 210 pp.

Lichens of North America, by Irwin Brodo, Stephen Sharnoff, and Sylvia Duran Sharnoff. Publisher: Yale University Press, 2001. 795 pp.

Gathering Moss, A Natural and Cultural History of Mosses, by Robin Wall Kimmerer. Publisher: Oregon State University, 2003. 168 pp.

Lichens above Treeline, A Hiker’s Guide to Alpine Zone Lichens of the Northeastern United States, by Ralph Pope. Publisher: University Press of New England. 2005. 70 pp.

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This page was last updated on January 25, 2008