The Difference Between Lichens and Mosses

19th November 2022

Whilst the ethos of Forest Bathing and Nature-Connection activities is usually about learning how nature makes you feel, rather than to learn about what something in the forest is, they are both also about encouraging curiosity about nature. So whilst we don’t often go on a Forest Bathing Walk to learn the names of trees (and mosses and lichen) it might still be something that we get a desire to learn more about once we are home.

Reindeer Cup Lichen, (Cladonia rangiferina), also called reindeer moss, a fruticose (bushy, branched) lichen found in great abundance in Arctic lands

Both mosses and lichens are cryptogams, which means that they reproduce through spores but without seeds or flowers, and both are non-vascular plants (see below). While they may often appear together, are frequently mistaken for each other, and are sometimes named ambiguously (see for example Oak Moss and Reindeer Moss which are in fact both lichens) they are actually quite different things! Both lichen and moss can grow on rocks, trees, plants and the ground, and both have previously been used as dyes, as food for animals, in medicines such as antibiotics, and in religious practices.

So, what is the difference between lichen and moss?

The Simple Answer

Simply speaking, a lichen is a combination of two organisms that co-exist together, and so are not really considered to be ‘plants’, whilst a moss is a single simple, quite primitive kind of plant called a bryophyte, but a plant none-the-less. Lichens lack leaves (or leaflets – see below) or stems of any kind, which helps to tell them apart from mosses. As plants, mosses can capture sunlight through photosynthesis in order to produce essential nutrients, whereas in lichen, it is the just the algae component of the combination that photosynthesises whilst the fungal component of the lichen grows hyphae into the cells of the algae to absorb these nutrients.

A More Complex Answer

Mosses

Mosses are one of the most primitive types of plant and their simple structure has remained largely unchanged over the millions of years of their existence. They are non-flowering plants that can produce spores but do not have true roots. Instead they have rhizoids which are small, hair-like structures that are used to anchor the moss to rocks, bark or soil. Some mosses suck up nutrients through their rhizoids, whilst others just absorb water and nutrients from around themselves using their capillary spaces like a big green sponge, which is why mosses are often found in very damp and humid places.

Mosses do have stems and ‘leaflets’ made of photosynthetic cells, a little like the leaves of trees and plants, although they may be so small that you need a magnifying glass to see them. ‘Leaflets’ are leaf-like structures, but they do not contain vascular tissue to transport water and nutrients up to the leaf tips- ‘leaves’ on the other hand do contain the specialised tissue needed to do this. However, this non-vascular structure allows some mosses that adapted to harsher environments to dry out and become dormant when it becomes too hot and to tolerate very low temperatures that other plants cannot.

Most mosses reproduce through spores that are cast out, although others reproduce from parts that are broken off the parent plant and scattered and then grow as a separate plant.

You can read a separate article that we have written all about the benefits of mosses!

Lichens

Usnea - a lichen

Lichens are a composite organism made up of a fungus and at least one algae or cyanobacteria. These two components exist together and behave as a single organism, living together and providing some benefit to the other, in what is referred to as a ‘symbiotic relationship’.

The algae (or ‘algal partner’ or ‘photobiont’) supply food and nutrients to the fungus through photosynthesis. Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize nutrients from carbon dioxide and water, generally involving the green pigment chlorophyll and generating oxygen as a by-product. In return for these nutrients the fungus (or ‘fungal partner’ or mycobiont) provides the body (or thallus) within which the algae lives and protects it from getting too hot or drying out.

According to the New York Botanical Gardens, it is debated whether the relationship in a lichen is mutualistic or part of a controlled parasitism. On one hand, the fungus and the algae appear to be in a mutualistic relationship because when they are combined, they have the ability to deal with ecological conditions that neither part would be able to handle on its own, and it seems that neither partner is damaged by the other. However, on close inspection, some might say that the photobiont is a captive of the mycobiont, not a partner, as the fungal partner ‘enslaves’ the photobiont to feed from its photosynthesis.

Some lichens produce spores in the same way a mosses, and these spores seek to connect with suitable partner algae or bacteria, and in the same way as mosses some lichens reproduce through breakage of the parent.

The Thallus of a Lichen

The thallus is the plant-like body or vegetative tissue of organisms in groups such as lichens, fungi, algae and some liverworts (more on them later!). It lacks differentiation into distinct parts such as stems, leaves, and roots and does not necessarily grow from the top of the plant.

Three Kinds of Lichen on Trees

There are three major types of lichen found on trees, Crustose, Foliose and Fruticose.

Crustose

Crustose lichens have a crust-like body (thalllus) and are tightly attached and cannot be removed without cutting the bark they grow on. They make up the majority of lichens on Earth, some of which grow on plants and trees and others only grow on rocks.

Foliose Lichen

Foliose

Foliose lichens have a thallus that is leaf-like (foliage-like) in both appearance and structure that is attached to the branch at the base, but they are usually easily removeable. They often grow on the ground or on trees and as such are the type most commonly mistaken for moss.

Fruticose

Fruticose lichens have a branched bushy, coral-like or shrub-like thallus attached to the branch by a sucker-like holdfast, and sometimes produce bright fruiting bodies. Fruticose lichens are most commonly found on trees.

Lichens as Environmental Indicators

Usnea - a sign of good air quality

Before the Industrial Revolution lichens would have been far more abundant. However, lichens are very sensitive to air pollution as they absorb most of their mineral nutrients from the air and rainfall and so can retain and accumulate large amounts of potentially damaging pollutants. Sulphur Dioxide (SO2) for example - which is produced by burning fossil fuels and smelting mineral ores such as aluminium, copper, zinc, lead, and iron that contain sulfur – can lower the pH of the lichen and lead to deterioration of chlorophyll causing photosynthesis to cease. Whilst there are lichens that tolerate pollution or even depend on it, many do not, and so lichens such as Usnea are a good indicator of the purity of the air and the health of the environment.

And then there are Liverworts and Hornworts too ….

As well as mosses the bryophyte family that mosses are a part of also includes Liverworts and Hornworts which will be discussed in a separate article.

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