Franz Joseph Andreas Nicolaus Unger (30 November 1800 in Gut Amthof near village Leutschach in Styria, Austria – 13 February 1870 in Graz) was an Austrian botanist, paleontologist and plant physiologist.

In 1820 he moved to Vienna to study medicine, in 1822 he enrolled at the Charles University in Prague.

From 1827 Unger practiced as a doctor in Stockerau near Vienna, then from 1830 as a court physician in Kitzbühel, Tyrol.

Unger was one of the major contributors to the field of paleontology, later turning to plant physiology and phytotomy.

He hypothesized that (then unknown) combinations of simple elements inside a plant cell determine plant heredity and greatly influenced the experiments of his student Gregor Johann Mendel.