Günther Ritter Beck von Mannagetta und Lerchenau[a] (25 August 1856 in Pressburg, modern Bratislava – 23 June 1931 in Prague) was an Austrian botanist.
Ritter Beck-Mannagetta, son of a state prosecutor, studied at the University of Vienna, where he graduated as Dr. phil.
After a period working as a volunteer at the Botanisches Hofkabinett, (later the Natural History Museum), he became head of the Botanical Department there from 1885 to 1899.
From 1899 to 1921 he was professor of systematic botany at the German Charles University in Prague and head of the Botanical Garden there.
published a genus of flowering plants from Siberia and China, belonging to the family Orobanchaceae, as Mannagettaea in his honour.