Ahti started developing an interest in botany at the age of 15, when he worked on a class project involving collecting 100 species of plants. His attention turned to lichens when a classmate who had worked for pointed them out during a birdwatching excursion in Helsinki. His interest was further fuelled when a couple of years later, he had to pass a test on identification of forest floor lichens and bryophytes as part of an application for work at the Finnish Forest Research Institute. He honed his identification skills during another summer job a few years later inventorying reindeer in Lapand. Ahti studied at the University of Helsinki, from where he earned an MSc in 1957, and a PhD in 1961. His thesis was entitled "Taxonomic studies on reindeer lichens ". He started employment in 1964 at the University of Helsinki Botanical Garden with the title Curator of Cryptogams, eventually working up to Deputy Head Curator of Phanerogams during 1965–1968, and then Head Curator of the Division of Cryptogams in 1969. In 1979, Ahti became a professor of Cryptogamic Taxonomy at the University of Helsinki, and a Research Professor at the Academy of Finland in 1991. Since retiring in 1996, Ahti has been a research associate with the Finnish Museum of Natural History in Helsinki. Ahti was president of the International Association for Lichenology from 1975–81. In addition to numerous research trips within Europe, he has also been to Asia, and North and South America. His Arctic lichen research expeditions have taken him to locations such as the Murmansk Coast, the northeast coast of Iceland, and the Sakha Republic. One of his favourite exotic locations was the tepui mountains of the Venezuelan Guayana, reachable only by helicopter. As of 2017, Ahti had more than 280 publications dealing with lichens, mosses, fungi, and phytogeography. Known as a specialist of the Cladoniaceae, he wrote a monograph on this subject for the journal series Flora Neotropica, which reviewer William Culberson called "the long-awaited fulfillment of an old promise by one of the world's master taxonomists." In the monograph, Ahti accepted 184 species of Cladoniaceae from the Neotropical realm, including 29 new taxa. Ahti made the numerous publications of William Nylander generally accessible through a five-volume reprint edition. Teuvo Ahti is married to botanist Leena Hämet-Ahti, who he met while they were both completing their MSc degrees. They married in 1960, and had a "honeymoon" in Wells Gray Provincial Park, where they collected several thousands of specimens of plants, mosses, liverworts, and lichens. In 1967, they collected 3000 specimens of vascular plants in Alaska, the Yukon, northern British Columbia, and Alberta.
Recognition
A festschrift was dedicated to Ahti in 1994 for his 60th birthday, titled Focus on Lichen Taxonomy and Biogeography: A Festschrift in Honour of Teuvo Ahti. Ahti was awarded the Acharius Medal in 2000, which is awarded for lifetime achievement in lichenology. He is an honorary member of the Russian Botanical Society of the Russian Academy of Sciences. In 2011, Ahti, along with co-authors, Katileena Lohtander, and Leena Myllys, won the Tieto-Finlandia Award for their non-fiction work Suomen jäkäläopas.
Eponymy
Four genera and several species have been named to honour Ahti. These include: Ahtia ; Ahtiana ; Teuvoa ; Teuvoahtiana ; Caloplaca ahtii ; Cladonia ahtii ; Hypotrachyna ahtiana ; Physma ahtianum ; Lecanora ahtii ; Parmelia ahtii ; Ramalina ahtii, Stenocybe ahtii ; Thelotrema ahtii ; Tuckneraria ahtii ; and Unguiculariopsis ahtii.
Selected publications
A complete listing of Ahti's scientific publications up to 2017 is given in Belyaeva and Chamberlain's tribute. Some of his major works include:
