The fine constructive work of Acharius appropriately begins a new era in the history of lichenology. Previous writers had indeed included lichens in their survey of plants, but always as a somewhat side issue. Acharius made them a subject of special study, and by his scientific system of classification raised them to the rank of the other great classes of plants.
Acharius was a country doctor at Wadstena on Lake Mälar in Sweden, as he himself calls it, “the country of lichens.” He was attracted to the study of them by their singular mode of growth and organization, both of thallus and reproductive organs, for which reason he finally judged that lichens should be considered as a distinct Order of Cryptogamia.
In his first tentative work[85] he had followed his great compatriot Linnaeus, classifying all the species known to him under the one genus _Lichen_, though he had progressed so far as to divide the unwieldy Genus into Families and these again into Tribes, these latter having each a tribal designation such as _Verrucaria_, _Opegrapha_, etc. He established in all twenty-eight tribes which, at a later stage, he transformed into genera after the example of Weber.
Acharius, from the beginning of his work, had allowed great importance to the structure of the apothecia as a diagnostic character though scarcely recognizing them as true fruits. He gave expression to his more mature views first in the _Methodus Lichenum_[86], then subsequently in the larger _Lichenographia Universalia_[87]. In the latter work there are forty-one genera arranged under different divisions; the species are given short and succinct descriptions, with habitat, locality and synonymy. No material alteration was made in the _Synopsis Lichenum_[88], a more condensed work which he published a few years later.
The Cryptogamia are divided by Acharius into six “Families,” one of which, “Lichenes,” is distinguished, he finds, by two methods of propagation: by propagula (soredia) and by spores produced in apothecia. He divides the family into classes characterized solely by fruit characters, and these again into orders, genera and species, of which diagnoses are given. With fuller knowledge many changes and rearrangements have been found necessary in the application and extension of the system, but that in no way detracts from the value of the work as a whole.