Lichenology
Some of his more important works on the subject, which marked the beginning of lichenology as a discipline, are: Later lichenologists include the American scientists Vernon Ahmadjian and Edward Tuckerman and the Russian evolutionary biologist Konstantin Merezhkovsky, as well as amateurs such as Louisa Collings.
[7] Against this background appeared the Swedish botanist Erik Acharius disciple of Linnaeus, who is today considered the father of lichenology, starting the taxonomy of lichens with his pioneering study of Swedish lichens in Lichenographiae Suecicae Prodromus of 1798 or in his Synopsis Methodica Lichenum, Sistens omnes hujus Ordinis Naturalis of 1814.
In these early years of structuring the new discipline various works of outstanding scientific importance appeared such as Lichenographia Europaea Reformata published in 1831 by Elias Fries or Enumeratio Critico Lichenum Europaeorum 1850 by Ludwig Schaerer[9] in Germany.
In Germany Hermann Itzigsohn [de][12] and Johann Bayrhoffer,[13] in France Edmond Tulasne and Camille Montagne, in Russia Fedor Buhse,[14] in England William Allport Leighton and in the United States Edward Tuckerman began to publish works of great scientific importance.
It was Anton de Bary a German mycologist who specialised in phytopathology who first suggested in 1865 that lichens were merely the result of parasitism of various fungi of the ascomycetes group by nostoc type algae and others.
[19] In 1873 Jean-Baptiste Edouard Bornet concluded form studying many different lichen species that the relationship between fungi and algae was purely symbiotic.
There appeared numerous renowned researchers within the field of lichenology such as Henry Nicollon des Abbayes, William Alfred Weber, Antonina Georgievna Borissova, Irwin M. Brodo, and George Albert Llano.
In 1982 the International Association for Lichenology convened a meeting to adopt a single definition of lichen drawing on the proposals of a committee.
The definition finally adopted was that lichen could be considered as the association between a fungus and a photosynthetic symbiont resulting in a thallus of specific structure.
For example, David L. Hawksworth considered the definition imperfect because it is impossible to determine which one thallus is of a specific structure since thalli changed depending upon the substrate and conditions in which they developed.
This researcher represents one of the main trends among lichenologists who consider it impossible to give a single definition to lichens since they are a unique type of organism.
Lichen is extremely sensitive to various air pollutants, especially to sulphur dioxide, which causes acid rain and prevents water absorption.
The discovery of various substances with antibacterial action in lichen thalli was essential for scientists to become aware of the possible importance of these organisms to medicine.
[27] From the 1940s there appeared various works by the noted microbiologist Rufus Paul Burkholder who demonstrated antibacterial action of lichens of the genus Usnea against Bacillus subtilis and Sarcina lutea.
With these investigations the number of antibacterial substances and possible drug targets known to be produced by lichens increased ergosterol, usnic acid etc.
These studies revealed some in vitro antitumour activity by substances identified in two common lichens Peltigera leucophlebia and Collema flaccidum.
