Methodus qua omnes detectos lichenes

Methodus qua omnes detectos lichenes is a foundational taxonomic work on lichens published in 1803 by the Swedish lichenologist Erik Acharius, with a supplementary volume issued shortly thereafter. The book revolutionised lichen classification by abandoning the single Linnaean genus Lichen and establishing 23 independent genera organised into orders, based primarily on the form and position of apothecia rather than microscopic features. Developed while Acharius worked in relative isolation in Vadstena, the work incorporated specimens from an extensive network of correspondents, including British botanists and material from Archibald Menzies' circumnavigations, and ultimately described 536 species. Although its publication was delayed by political tensions between Britain and Sweden, the Methodus was championed in England by Dawson Turner and James Edward Smith, who recognised it as essential for managing the rapidly expanding knowledge of lichen diversity. Despite later criticism of its morphology-centred approach, the work established principles that remain fundamental to modern lichen taxonomy, and Acharius's annotated specimens continue to serve as important reference material for contemporary systematic studies.

The title translates to: "A method by which Erik Acharius attempted to arrange all discovered lichens into genera, species and varieties according to their reproductive organs, and to illustrate them with observations."

Publication

Methodus qua omnes detectos lichenes was published in Stockholm in 1803, with a supplementary volume (Supplementum) issued later from Leipzig.^[1] The book, printed in Stockholm by C.F. Marquard for F.D.D. Ulrich and prepared under the supervision of Professor Schrader at Göttingen, marked a clear break from Linnaean practice by splitting the single genus Lichen into a series of independent genera.^[2] By October 1802, about two-thirds of the manuscript had been sent to the publisher.^[3] Political difficulties between Britain and Sweden during this period hampered distribution, and copies were slow to reach British botanists.^[4]

As Acharius explained in the preface to the Supplementum, most of the main volume was already in print when he received a manuscript from Göran Wahlenberg describing numerous new northern species from the 1802 expedition, so he had this material issued a few months later as a separately paginated supplement, printing Wahlenberg's diagnoses almost verbatim and appending brief comments of his own.^[5][6] Modern nomenclatural work has shown that the 27 new lichen names introduced there, including ecologically important northern species such as Verrucaria maura and Parmelia elaeina, should be cited as "Wahlenb. in Ach." because Acharius explicitly treated Wahlenberg as the author of the diagnoses.^[6]

Content

The Methodus introduced a revolutionary taxonomic arrangement that separated lichens into distinct genera, moving beyond the previous Linnaean system that grouped all species under the single genus Lichen.^[7] Acharius organised 23 genera and 536 species into orders, defining the genera by apothecial position and form and using thallus structure only at subgeneric level. Like his later systematic works, he based these taxa almost entirely on macroscopic features visible without a microscope, such as overall thallus form and the shape and position of the apothecia. This morphology-centred approach made the system practical for field workers but left anatomical characters largely unexplored.^[8] The work incorporated specimens from diverse geographical sources, including collections from British botanists and material gathered during Archibald Menzies' circumnavigations of 1786–89 and 1791–95.^[1]

Acharius provided detailed descriptions of new species, including several collected by Menzies from New Year's Harbour on Isla de los Estados, Staten Land, and British Columbia.^[9] Among these were Hypogymnia enteromorpha, Menegazzia cincinnata, Hypogymnia duplicata, Leptogium menziesii, Nephroma cellulosum, and Pseudocyphellaria obvoluta.^[9] However, some geographical locations were incorrectly attributed in the text, such as Staten Land being mistakenly listed as Ad Fretum Magellanicum, an error that has caused subsequent confusion for taxonomists attempting to typify Acharian taxa.^[10]

The taxonomic descriptions in the work were later expanded in Acharius's subsequent publication, Lichenographia universalis (1810).^[7]

Development

Acharius developed the Methodus while working in relative scientific isolation in the Swedish town of Vadstena (Östergötland).^[7] Owing to his remote location, he relied heavily on his colleague Olof Swartz in Stockholm for access to lichen specimens from foreign countries.^[7] Swartz, who had visited England in 1788, maintained valuable connections with the Banksian Herbarium, Sir Joseph Banks's extensive private herbarium in London, and with British botanists through his countryman Jonas Carlsson Dryander.^[1] Acharius's friendship with Swartz provided not only specimens but also a sustained forum for testing ideas: more than 300 surviving letters between 1792 and 1815 show Acharius repeatedly sounding out his concepts of lichen classification, and in an August 1793 letter he first set out to Swartz the central role he intended fructification to play in defining genera, a principle later elaborated in his published systems.^[11]

The work's development benefited from an extensive network of correspondents, including the British botanists James Edward Smith, Dawson Turner, William Borrer, John Harriman, and Nathaniel Winch.^[7] These connections were particularly important for obtaining specimens, with Smith and Turner regularly sending British lichens to Acharius through Swartz.^[1] The manuscript development took several years, with Swartz reporting in September 1802 that Acharius was "working on a general synopsis of the Lichens which will be good".^[12]

The work was also shaped by specimens collected during scientific expeditions, notably those gathered by Archibald Menzies during his two circumnavigations.^[1] These specimens helped broaden the geographical scope of Acharius's taxonomic understanding.^[9]

Reception and influence

The Methodus was first championed in England by Dawson Turner and James Edward Smith, who were instrumental in introducing Acharius's new taxonomic system to British lichenology.^[13] In a lengthy 1804 review in the Annals of Botany, Turner presented the book as the natural successor to the Lichenographiæ Suecicæ Prodromus, arguing that the rapid increase in known lichen species since Linnaeus made a subdivision of the old catch-all genus Lichen unavoidable. He explained to English readers how Acharius now defined genera by the form, texture, and attachment of the apothecia, segregated doubtful species, named major varieties, and used engraved plates and a glossary of new terms to make the system workable, remarking that such a generic treatment of lichens had "never before … been treated of by any English writer". Turner praised the Methodus as "the most excellent work we ever read upon the Lichens", while expressing doubts about some of the more finely split crustose and Parmelia species and warning that extensive changes to specific names and the proliferation of new Greek coinages threatened to throw nomenclature into "chaos".^[14][13]

Smith's initial response was more conservative. While acknowledging the work's importance, he expressed reservations about changing established nomenclature, noting that he "must keep in view those Laws of Linnaeus which are sanctioned by experience and founded in justice".^[15] Despite these concerns, he actively corresponded with Acharius and contributed specimens for study.^[9]

The work's influence spread through a network of correspondence between Swedish and British botanists.^[1] Its impact on English lichenology was considerable, influencing subsequent generations of botanists including William Borrer, who carefully examined Acharius's specimens after their arrival at the Linnean Society of London.^[16] The taxonomic concepts introduced in the Methodus continue to have relevance for contemporary studies in lichen taxonomy.^[17]

Legacy

The Methodus established the foundations of modern lichen taxonomy through its pioneering approach to generic classification.^[7] The specimens Acharius examined and annotated while preparing the work remain fundamentally important for contemporary taxonomic revisions.^[7] These specimens, now housed in the British Museum (Natural History), were purchased from the Linnean Society of London in 1963 and continue to serve as important reference material for researchers.^[18]

The collection consists of 894 specimens arranged across 41 genera, representing Acharius's taxonomic arrangement as used in his later work Lichenographia universalis.^[19] The specimens are attached to water-marked paper glued on cards measuring 11–12 × 7–8 cm, and are housed in packets mounted on herbarium sheets and enclosed in folders following their original catalogued order.^[16] This material is particularly valuable because it demonstrates the evolution of Acharius's taxonomic concepts, with specimen labels showing revisions from the Methodus system to that of his later publications.^[19] The only limitation of this historic collection is the absence of collector and locality information for the specimens.^[16]

Subsequent nineteenth-century systems, such as that of Abramo Bartolommeo Massalongo, criticised Acharius's reliance on apothecial form and position and shifted attention towards ascospore characters, yet modern authors still treat the Methodus, together with Lichenographia universalis and Synopsis methodica lichenum, as one of the principal early cornerstones of lichenology because it abandoned Linnaeus's single genus Lichen in favour of a more natural suite of generic entities.^[8] The work's significance extends beyond its time, having influenced subsequent generations of lichenologists and established taxonomic principles that remain relevant to modern systematic studies.^[17]