Gustav Karl Wilhelm Hermann Karsten (6 November 1817, in Stralsund – 10 July 1908, in Zoppot) 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 (Venezuela, Ecuador and Colombia). 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 (1868–72). He died 1908 in Berlin-Grunewald.
As a taxonomist, he was the binomial author of many botanical species.