Johannes Reinke (February 3, 1849 – February 25, 1931) was a German botanist and philosopher who was a native of Ziethen, Lauenburg. He is remembered for his research of benthic marine algae.
He studied botany with his father from the age of eight. Reinke studied theology at , but his focus later changed to botany. In 1879 he became a professor of botany at the University of Göttingen, where he established the institute of plant physiology. From 1885 until 1921, he was a professor at the University of Kiel. Reinke was a co-founder of the Deutsche Botanische Gesellschaft.
Reinke had a keen interest in the systematics, developmental cycles, cytology and physiology of brown algae. From 1888 to 1892 he published a number of articles on marine algae from the North and Baltic Seas — in regards to the Baltic, he described several new genera of algae. He also published works on the algal families Tilopteridaceae (1889) and Sphacelariaceae (1890). Furthermore, he postulated that the encrusting algae genus called Aglaozonia was a stage in the life history of Cutleria. The genus Reinkella (family Roccellaceae) is named in his honor.
Reinke was a proponent of scientific "neo-vitalism", and a critic of the Darwinian theory of evolution. Opposing the secularization of science, Reinke, along with his Lutheran friend , founded the Kepler Union in order to counteract Haeckel's Monist League which aimed to "replace" German churches with the evolutionary theory as a secular religion.