Siegfried Jost Casper (12 January 1929 – 13 June 2021) was a German biologist whose primary research was in limnology and the plant genus Pinguicula (the butterworts). Together with Heinz-Dieter Krausch he published a basic reference work on the freshwater flora of central Europe. For many years he studied the East German lake Stechlinsee as well as the river Saale. In 1966 he published a monograph of the genus Pinguicula, a work that is still in use today. He described at least 14 new species, most recently Pinguicula lippoldii and Pinguicula toldensis in 2007.[1] He served as head of the Botanical Garden of the Friedrich Schiller University of Jena and from 1990 until his death was a member of the "Akademie Gemeinnütziger Wissenschaften" in Erfurt.