The Greek word leichḗn he came to Latin as lichen, which in our language derived in lichen . This is called a organism that arises from the symbiosis of unicellular algae with fungi .
This symbiosis It occurs when the fungus absorbs nutrients from the algae. For this it is common for the fungus to penetrate the algae cells through the haustorios : the tips of the hyphae (the network of filaments that are part of the fungus structure). Once the symbiosis is completed, lichen feeds on the substances that the algae synthesizes through photosynthesis.
Lichens develop in humid environments , growing like scabs or sheets in barks of trees or on stones. According to the type of association that establish algae and mushrooms , present different structural characteristics.
Thanks to their resistance, lichens can develop colonization of different kinds of ecosystems. The symbiotes can perform photosynthesis like algae and, in turn, they are protected against sun radiation like fungi. With the so-called liquid substances, in the meantime, lichens can take advantage of light and water efficiently.
Lichens have been found in deserts and in polar regions , for example. Their adaptability allows them to subsist and develop in multiple habitats. Experiments were even carried out that showed that lichen can subsist in the outer space without protection.
It is important to mention that the taxonomic classification of lichen is usually a matter of discussion. The specialists have included these organisms in different groups throughout history.
Regarding the history of lichens, it should be noted that their fossil remains appear very infrequently. In the field of paleobotany , the discipline that merges botany and paleontology with the aim of studying the remains of ancient plants, it is known that an incomplete record is not enough to teach us the reality of flora in a time remote
When traces are scarce, therefore, they are used to estimate at what time in history the species to which they belong. This research is carried out using the knowledge and techniques of the phylogeny (the relationship of kinship between species or taxa). In this particular case, that of lichens, the point in time is sought at which a fungus and an algae crossed the aforementioned symbiosis for the first time.
So far, the Thuchomyces lichenoides It is considered the oldest lichen. It is believed that he appeared in the Precambrian, the first stage of the history of our planet and also the most extensive. It was a marine species, according to the sediments in which its fossils were found. Scientists have not been able to determine if there was a photobiont linked to this lichen, although they did identify their mycobiont.
At the site of Rhynie chert , on the other hand, a fossil was found that they have called Winfrenatia reticulata, whose scientific value is incalculable since it places it in the period devout , which corresponds to the Paleozoic Era .
The reproduction of lichens can occur asexually by means of thallium portions of both biontes. This term, which is also known as "fake tissue", is defined as the group of leaves, stem and root of a plant; in the case of algae, on the other hand, it is composed of sheets, haptera and stipe. This asexual reproduction takes place in the so-called "talin fragmentation". It can also be done through the soredios and the isidios, two specialized structures.