The system of lichen taxonomy devised by the Swedish botanist Erik Acharius in his Methodus qua omnes detectos lichenes (1803) was introduced into English lichenology by Dawson Turner and James Edward Smith. At the instigation of Olof Swartz in Stockholm, both Smith and Turner corresponded with Acharius and sent him lichens from Britain, and from British explorations in the Pacific and North America. The influence of Acharius and Swartz on the development of lichenology in England in the early years of the 19th century is here traced through unpublished contemporary correspondence between Acharius and Swartz in Sweden, and Smith and Turner in England. The circumstances surrounding Acharius's important gift of lichens to the Linnean Society of London [now in the herbarium of the British Museum (Natural History)] are described, and a list of the lichens in BM-ACH appended.