mammadaba - Lichens – peculiar decoration of tree stems

“What are those stains on tree stems?” a group of children asked me one time during a hike through forest.

And sometimes it happens that people, already adults, never have paid attention and as it turns out, have no idea, that those stains on tree stems are not ordinary bark stains, but are specific growing organisms – lichens – each of them with their own name.

Lichens are unique organisms, in whose largest thallus part (vegetative part of lichens) an interaction between fungi and algae is taking place. The fungi receive organic matter from algae, however, algae from fungi – water and nutrients. They supply each other with necessary, thus, lichens can grow in places that do not provide any nutrients by themselves, even on such artificial materials as plastic and glass.

Lihens can be classified, grouped differently. One of ways of how to group lichens is on the basis of their morphological or thallus visual appearance. The widely known groups of this division are

Crustose lichens;

Foliose lichens;

Squamulose lichens;

Fruticose lichens.

Crustose lichens

The thallus of the lichen is strongly adhering to substrate or is even grown into it, thus, looks like a stain of different colour or can’t even be noticed. More easily noticeable are the fruiting bodies – organs, where spores are produced. They can be different – as dark or light spots, as small volcanoes or needles.

Such lichens as rim lichen (Lecanora), lecidellas (Lecidella), script lichen Graphis scripta are widely distributed on tree stems.

The special protection species - Arthonia leucopellea – fruiting bodies have grown together, sometimes look like cat paws (Photo: O.Demiters)

The special protection species - Thelotrema lepadinum – fruiting bodies look like small volcanoes (really small! Their size is 1 – 4 mm) (Photo: O.Demiters)

Foliose lichens

These lichens can be noticed from a larger distance than the previous ones, because their thallus can be even up to ten centimetres big. It looks like leaves or flat lobes, often are ridged. Several species are attached to surfaces with special root like structures – rhizines.

The special protection species – tree lungworth Lobaria pulmonaria – usually can be found in old, unaffected biotopes (Photo: O.Demiters)

Squamulose lichens

The thallus of these lichens is usually composed of small, flat, clustered scales, which frequently overlap. Scales are attached to substrate, but edges are a little raised. Sometimes this type of lichens is mistaken for foliose lichens, however, their thallus usually is smaller and they don’t have pronounced underside skin.

Fruticose lichens

These lichens look like small shrubs. Depending on the substrate they can grow upwards, to the sides or downwards. This type of lichens frequently reproduces from broken off pieces of the thallus. The broken off thallus piece, when lands in an appropriate environment, attaches to substrate and continues to grow.