[2] Acharius's dissertation titled, Planta Aphyteia, was on a vascular plant species (Hydnora) collected in Southern Africa by Carl Peter Thunberg, which Linnaeus incorrectly classified as fungi.

[5] Acharius spent the remainder of his life in Vadstena, where he died of a stroke while in his household garden examining a Spanish collection of lichens on 14 August 1819, at the age of 61.

[2] Acharius belonged to the younger generations of Swedish botanists who continued what Linnaeus had left undone; classifying all living organisms.

While composing Lichenographiae Suecia prodromus, Acharius began communicating with Olof Swartz, another Linnaean disciple, and from 1780 to 1815 they sent nearly 350 letters to each other.

[8] Additionally, Swartz introduced Acharius to many other Swedish naturalists as also several important international figures such as James Edward Smith, the head of the Linnean Society.

After publishing his first work, he sent a copy to James Edward Smith who, in response, inducted Acharius as a foreign member of the Linnean Society.

[9] Subsequently, Acharius published Methodus qua omnes detectos Lichenes (1803),[10] Lichenographia universalis (1810),[11] and Synopsis methodica lichenum (1814)[12] each of which he sent to the Society in London, accompanied by hundreds of the specimens described in each book.

In 1804 Friedrich Weber (1781–1823) and Daniel Matthias Heinrich Mohr (1780–1808), two German naturalists, published Naturhistorische Reise durch einen Theil Schwedens which heavily featured his work on lichens and also included four illustrations by Acharius.