Franz Julius Ferdinand Meyen (28 June 1804 – 2 September 1840) was a Prussian physician and botanist.
Meyen was born in Tilsit, East Prussia. In 1830 he wrote Phytotomie, the first major study of plant anatomy. Between 1830 and 1832 he took part in an expedition to South America on board the Prinzess Luise, visiting Peru and Bolivia, describing species then new to science such as the Humboldt penguin.
From 1823 to 1826 he studied medicine at the University of Berlin, followed by service as a military surgeon at the Charité in Berlin. In 1834 he became an associate professor of botany in Berlin. With Heinrich Friedrich Link, he was co-editor of the journal "Jahresberichte über die Arbeiten für physiologische Botanik" (1837-1839).
The plant genus Meyenia commemorates his name.
He died in Berlin in 1840.