Gunnar Bror Fritiof Degelius (né Nilsson until 1932; 27 January 1903 – 22 July 1993) was a Swedish lichenologist.

[3] After his family moved to Gothenburg, he met the lichenologists Captain Carl Stenholm and Adolf Hugo Magnusson, both of whom encouraged his early interest in lichens.

They shared an early interest in natural history, and they would often go on trips together to collect plants, beetles, and lichens in Mölndal, south of Gothenburg.

[4] Degelius matriculated in 1923, the same year he published his first scientific paper (under the name Nilsson) on the lichen Arthonia spadicea.

[2] His professor of systematic botany became aware of Degelius because of his tendency to frequently miss lectures; after he called him into his office for an explanation, it became evident that Degelius already knew the subject matter quite well, having essentially memorized the textbook used for the course, Eduard Strasburger's Lehrbuch der Botanik.

[6] It was at Uppsala university that Degelius associated with the professor Rutger Sernander at the Växtbiologiska Institutionen (Institute of Botany), from where he graduated in 1935 with a dissertation titled Das ozeanische Element der Strauch-und Laubflechtenflora von Skandinavien ("The oceanic element of the shrub and lichen flora of Scandinavia").

He worked under the supervision of Professor Gustaf Einar Du Rietz, along with Sten Ahlner, Torsten Hasselrot, and Rolf Santesson – all of whom became notable lichenologists.

[5] After his retirement, Degelius travelled the world, visiting exotic locations on several continents to continue his lichen studies.

[5] In her obituary of Degelius, Polish lichenologist Jolanta Miądlikowska described him as belonging "to the group of scholars who are appreciated not only for their knowledge and scientific achievements, but also for 'humanity'".

He had a lichenological library comprising more than 45 metres (148 ft) of shelf space, including original classic works by Carl Linnaeus, Erik Acharius, Elias Magnus Fries, and others.

[2] The New Zealander botanist David Galloway, who attended a class of Degelius' in the 1960s, recalled the atmosphere at one of the frequent gatherings there: "Very many will remember the warmly convivial discussion in the spacious book-lined sitting room with candles lit, a bottle of port or punch open on the table, and the cigars circulating.

It was a warmly welcoming and special ambience which was very much part of Gunnar ... the celebrated photograph albums of past and present lichenologists would be produced, recent publications would be discussed, minutes would fly past into hours and by midnight when the guests were wilting, Gunnar would just be getting into his stride.