Gustav Karl Wilhelm Hermann Karsten was a German botanist and geologist.
Born in Stralsund, he followed the example of Alexander von Humboldt and traveled 1844-56 the northern part of South America. From 1856 to 1868, he was a professor at the agricultural college in Berlin, afterwards serving as a professor of plant physiology at the University of Vienna. In 1881, at the suggestion of David Friedrich Weinland, Karsten became convinced of the correctness of Otto Hahn's organic theory of the chondrites and, as a result, wrote an essay entitled "Die Meteorite und ihre Organismen" in which he declared his support for Hahn's theory. He died 1908 in Berlin-Grunewald.
As a taxonomist, he was the binomial author of many botanical species.