I know several people who work tirelessly in the background doing all the hard and dirty work, making sure the day to day activities get done, and keeping things running; but NEVER GET THE CREDIT! Never get a ‘that a boy” or “great job”. This is the case with two members of the plant kingdom, mosses and lichens. This article is my feeble attempt to give credit where credit is due and thank those unappreciated, hard working members of the plant kingdom.
There are about 24,700 species of bryophytes — mosses, liverworts, and hornworts in the world and no one really know how many lichen species there are. However it is estimated that lichens are the dominant vegetation on 8% of the earth’s terrestrial surface. Yes 8% and you probably have never paid much attention to these interesting plants. Both of these groups are highly adapted to a diversity of terrestrial environments, even deserts!
In order to begin to understand these two different plant groups we need to start with some basic botany. All living plants can be organized into four distinct groups: Non-Vascular (no xylem or phloem), Seedless vascular plant (Ferns), Gymnosperms (Conifers), and Angiosperms (Flowering plant). Both Bryophytes and Lichens fall in the first group. As mentioned earlier, we will focus on one of the bryophytes, the mosses; sorry liverworts and hornworts. Although moss and lichens are both called non-vascular plants, only mosses are plants. Lichens and mosses have a few things in common, size, and habitats. Mosses retain water, which is what lichens use to prolong their growth cycle. That’s why most lichen will have mosses growing along side of them and vice versa.
Lichens do not have any roots, stems, or leaves. Everything in the lichen’s environment is absorbed into the lichen’s structure. Lichens get their water and nutrients from their surrounding environment via air and rain. Lichens are a complex life form that is a symbiotic partnership of two separate organisms, a fungus and an alga; “that took a LIKEN to one another.” Sorry could not resist that naturalist gem! The dominant partner is the fungus, which gives the lichen the majority of its characteristics, from its thallus shape to its fruiting bodies. The alga can be either a green alga or a blue-green alga. Many lichens will have both types of algae. The general structure of lichen is composed of layers of fungus and alga. The cortex is the outer layer of the lichen thallus. These cells are thicker and more closely packed than the other fungal cells in the lichen. Green algae generally give the lichen a bright green color when wet. Cyanobacteria can be a layer under the upper cortex or in tiny pockets on top of the upper cortex if there is a green algal layer already present. Cyanobacteria will give the lichen a dark green, brown, or black color. In many cases lichens are pioneer species. Rhizines are fungal filaments that extend from the medulla and attach the lichen to its substrate. The rhizines of the lichen break down exposed rocks or wood, producing soil particles and releasing nutrients for the use of more complex plants that succeed them.
Most mosses are small; few exceed 7 centimeters in height. Mosses have spread all around the world and are found in wet environments such as rainforests, wetlands, and alpine ecosystems. They are also common in urban areas with a wet climate and often establish on driveways, sidewalks, brick walls and other man-made structures. Mosses require water to reproduce which is why they struggle to survive in drier climates. They are best known for those species that carpet woodland, rock walls and forest floors. They also aid in soil erosion control by providing surface cover and absorbing water, and they are important in the nutrient and water economy of some vegetation types. Economically important species are those in the genus Sphagnum that form peat. In order to reproduce, mosses produce spores for reproduction instead of seeds and don’t grow flowers, wood or true roots. Instead of roots, all species of moss have rhizoids. In many cases mosses are called pioneer species within an ecosystem. Similar to the rhizines of the lichens, rhizoids of mosses break down exposed rocks or wood producing soil particles and releasing nutrients for the use of more complex plants that succeed them.
One of the ways lichens directly benefit humans is through their ability to absorb everything in their atmosphere, especially pollutants. Lichens can provide us with valuable information about the environment around us. One of the first pollution studies was done in London. The study found that there were no lichens near the mills and industrial sites. It was determined that the farther they moved from these sites, the more lichens they found, thus making lichens are a good indicator of air quality. Mosses are also very important to the environment. They perform a number of functions that help ecosystems perform effectively such as filtering and retaining water, stabilizing the ground and removing CO2‚ from the atmosphere.
So, next time you go out and enjoy Nearby Nature, pay attention to the mosses and lichens. Some are exceptional, like these British Soldier lichens. Thank them for their hard work and give them some love, they have earned it!