Jahnula is a genus of aquatic fungi in the family Aliquandostipitaceae. The genus was first named by Wilhelm Kirschstein in 1936. The genus name of Jahnula is in honour of Eduard Adolf Wilhelm Jahn (1871-1942), German botanist (Mycology) and teacher in Berlin. The genus was circumscribed by Wilhelm Kirschstein in Ann. Mycol. vol.34 on page 196 in 1936.