In 1915, Von Wettstein characterized Geosiphon pyriforme as a multinucleate alga containing endosymbiotic cyanobacteria, although he also noted the presence of chitin, a component of fungal cell walls. In 1933, Knapp was the first to suggest the fungal origin of the species and described it as a lichen with endosymbiotic cyanobacteria.
In 1915, Von Wettstein identified Geosiphon pyriforme as a multinucleate alga containing symbiotic cyanobacteria, but also noted the presence of chitin, a component found in fungal cell walls. In 1933, Knapp proposed that Geosiphon pyriforme was a fungus with endosymbiotic cyanobacteria.