Gustav Niessl von Mayendorf (26 April 1839 in Verona – 1 September 1919 in Hütteldorf, Vienna; often cited as G. von Niessl), was an Austrian astronomer and mycologist.
[1] Niessl, the son of an artillery officer, studied at the Polytechnic in Vienna in 1857 and became assistant to practical geometry.
As an astronomer, he was employed with Niessl meteor orbits and also wrote the article in the Enzyklopädie der mathematischen Wissenschaften (Encyclopedia of Mathematical Sciences) (1907).
He was regarded as an expert in the flora of Moravia and Silesia, and had close contact with the botanist Gottlob Ludwig Rabenhorst.
He was particularly concerned with microscopic sac fungi, slime molds, and rusts.