Johannes Rein, a German geographer, geologist and teacher, made botanical collections during many travels around the world, notably in Japan in 1873-1875.

Rein was born in Raunheim bei Giessen and studied mathematics and sciences at the University of Giessen. Following a period as a school teacher in Reval and Dorpat (1858-1860) he travelled in the Baltic region and Russia. Producing studies of climate, soil and vegetation in Estonia, in 1861 he gained a doctoral qualification at the University of Rostock. In the same year he travelled to England, where he was appointed private tutor in the house of the new governor of Bermuda, where he lived until 1863.

Returning to Germany, Rein settled in Frankfurt, where he took an active part in the Senckenberg natural history society, while working as a teacher until 1872.

Rein made several scientific expeditions, travelling with Krl von Fritsch in the Canary Islands and Morocco in 1872 and Japan in 1873-1875. The latter, a government-sponsored expedition, resulted in Rein's works Japan, nach Reisen und Studien (1881-1886), translated into English as Japan, Travels and Researches (1884-1889), and Briefe eines deutschen Geographen aus Japan 1873-1875 (Letters from a German geographer in Japan), published in 1889.

After his return from Japan Rein was appointed Professor of Geology at the University of Marburg and in 1883 transferred to Bonn. From 1900 he taught economics in Cologne. He also made journeys in Spain, Scandinavia and North America.

Sources:
U. von den Driesch, 2003, "Rein, Johannes Justus", Neue Deutsche Biographie, 21: 341
J.J. Kerp, 1918, Geographische Zeitung, 24: 331-342.