After reading this article, you will learn what lichen consists of, what forms of these plants are found, and also what role they play in nature and in the economic activity of people. We will also talk about how they absorb moisture, and describe their metabolism.
Where do lichens grow?
Lichens are adapted to life even in the most severe conditions, often they are fixed where other living organisms cannot exist. They go north and south further than other plants. In the Himalayas, they were found at heights of more than 5600 m.
Lichens, examples of which are numerous, can exist on almost any surface, whether it is a sun-scorched rock, an anhydrous desert, the back of a beetle or the bleached bone of a fallen animal. One species (Verrucaria serpuloides) lives for a long time plunging into the icy waters of the Antarctic, the other (Lecanora esculenta) is carried by the wind. And although lichens are generally very sensitive to all kinds of industrial waste, a species like Lecanora conizaeoides thrives markedly in fairly polluted places.
Lichen Forms
In accordance with the characteristics of growth, all known species of these plants (and there are 15,000) are divided into three main groups. We briefly describe each of them.
Leafy flourish in areas characterized by heavy rainfall. As you probably already guessed, they are named so because they resemble leaves in shape. One of their species is presented in the photo below.
The next group - scale (cortical). They are resistant to drought and therefore prevail in deserts. Scale lichens adhere closely to the substrate on which they grow. Caloplaca heppiana, for example, is often found on walls and gravestones. This and a number of similar species of plants of interest to us are used as indicators of the age of the substrate. Lichens of this group are often brightly colored, and the fungus is pigmented.
And finally, bushy are able to take moisture from the air and are mainly in areas of humid climate. The sizes and appearance of the plants of interest to us are very diverse. Some of them form threads of 2.75 m or more in length, while others are no larger than a pin head.
What does lichen consist of?
These organisms are formed from plants belonging to two different departments: from algae and fungus. We will tell you more about what lichen consists of. He is one of the most successful examples of mutualism. This term refers to a mutually beneficial partnership that can be established between two dissimilar organisms.
The algal component is a necessary element of what lichen consists of. These are usually either green or blue-green algae. The fungal component is a representative of marsupials, or ascomycetes. With rare exceptions, only those plants that consist of one species of fungus and one species of algae are classified as lichens. Of the latter, the composition of these plants (more than 50% of the species) most often includes the unicellular green alga Trebouxia, but there may be others.
So, lichens include organisms consisting of fungus and algae, which are in mutually beneficial cohabitation. We give one more example. Xanthoria parietina (pictured below) is usually found on cliffs along the sea coasts, as well as on the walls and roofs of houses. Its orange saucer-shaped fruiting bodies (apothecia) are almost indistinguishable in structure from the fruiting body of an isolated fungus.
A thin top layer of densely intertwined fungal hyphae can be seen in the lichen section. It includes individual cells of green algae. Basically, a lichen is an organism whose body consists of loose intertwined fungal hyphae, below which is another thin layer of hyphae, similar to the upper one.
Lichen growth
They grow very slowly. Most scale species rarely increase in size over the year by more than 1 mm. Other forms of lichens grow a little faster, but they add no more than 1 cm per year. It follows that large species of these plants have a very respectable age; Some individuals in some arctic species are believed to be older than 4,000 years.
Using the so-called lichenometry, i.e. measuring lichens, even determine the age of the surface of the rocks. This method was used to establish the age of glaciers, as well as giant megaliths (large stone blocks). The latter were found on Easter Island in the Pacific.
The solid age of these plants shows that they have a fairly high organization and that the relationship between algae and fungus is well balanced. But the true nature of this relationship is not yet entirely clear.
Metabolism
The photosynthetic alga, like other green plants, provides food for both partners, since the fungus does not have chlorophyll. Simple carbohydrates synthesized by algae are secreted by it and are absorbed by the fungus, where they are converted to other carbohydrates. This carbohydrate metabolism underlies the symbiotic relationship that led to the formation of lichen. The transfer of nutrients from algae to the fungus occurs very quickly: it was found that the mushrooms manage to convert sugars from the algae within three minutes from the start of photosynthesis.
Moisture absorption
Lichens, absorbing a lot of moisture, vary significantly in volume. Their height significantly increases. Separation of organs that give and absorb moisture in these plants is absent. The bark performs both of these functions. Lichens also have no devices that protect them from transpiration, which are well developed, for example, in vascular plants. Most organisms of interest to us receive moisture from the air, not from the soil. They absorb water vapor. Only some species attached to the substrate have the ability to take part of the moisture from it.
The use of lichens
Lichens in nature find various uses: they serve as food for animals (for example, make up two-thirds of the reindeer’s diet), are used by birds as nesting materials, and serve as a refuge for many species of small invertebrates, such as ticks, beetles, butterflies and snails. They bring benefit to man. Lichen extracts were once used to dye fabrics from which Scottish skirts were sewn . Of these, yellow, brown, red and purple were obtained.
paints. Intermediate colors were obtained by staining.
Icelandic moss (Cetraria islandica) has been used as a cough suppressant for more than two centuries. Human usnic acid present in some lichens is used to treat superficial wounds and tuberculosis.
Modern research has found in them antibiotics that are effective against diseases such as pneumonia and scarlet fever. In addition, these plants are used in industry. So, from lichen Roccella sp. a special litmus is extracted - a chemical indicator that turns red in an acidic environment and blue in an alkaline one.