German botanist, zoologist, physician and philosopher from Schloß Reichenberg bei Reichelsheim (Odenwaldkreis). He studied medicine, natural history and philosophy at Jena (1796-1799), was promoted to doctor of medicine in 1800 and practiced in Frankfurt for a while, but soon returned to science. He joined the prestigious Leopoldina Academy in May 1816 and was appointed professor of botany at Erlangen (1817), and soon after was elected life president of the Leopoldina Academy (1818). He was appointed a professor of the University of Bonn and became director of the botanical garden in Bonn (1818-1830). His botanical work was prolific and included an early publication on freshwater algae (1814), publications of mycology and bryology and a manual of Botany (1820-1821) that contained some controversial theoretical concepts. His monographic work includes accounts of the Asteraceae (1831, 1831) and Lauraceae (1836). He published on the cryptogamic collections of Blume and Reinwardt from Indonesia and also contributed accounts of cryptogams, Poaceae, Cyperaceae and Acanthaceae to the Flora Brasiliensis of Martius. His contribution to African botany is based mainly on the accounts of Acanthaceae, Lauraceae, Piperaceae, Poaceae and Solanaceae for the Enumeratio Plantarum Capensium of Ecklon.
The marriage to his first wife Wilhelmine von Ditfurth (1802) was short as she died in the following year and his second marriage to Jacobine Elisabeth von Mettingh (1804) resulted in five children. The academic position at Bonn came to an end following an affair with the wife of another professor at the university. Divorce laws in Bonn prevented him from marrying his third wife so he negotiated with his friend the botanist Ludolph Christian Treviranus at Breslau to exchange the two professorships. After receiving ministerial permission, he started lecturing in Breslau in 1830. His divorce took place in 1830 but he was only able to marry his third wife in 1833 after overcoming many obstacles. The climate in Breslau had an adverse effect on his health and he tried to return to Bonn but his request was turned down. His third marriage ended in separation (1839) and he went to live with his cook, Christiane Kambach.
During his time in Breslau, Nees became increasingly radical in his political outlook. He first met the philosopher, poet and polymath J.W. Goethe in 1819 at Weimar, who influenced him greatly and was a regular correspondent. The genus Goethea Nees was named in honour of the philosopher. Nees became politically active in 1848 with a socialist bill brought before the Prussian National Assembly. He was elected president of the worker's union in Berlin (1848) but soon came into conflict with the government who considered him a dangerous socialist. He lost his position as professor at the University of Breslau and his pension (1852), which led him into poverty. His library and herbarium of some 80,000 sheets were sold around this time to cover the cost of mounting debts but no single buyer could be found and the herbarium was broken up. Material attributed to Nees von Esenbeck from Africa and Indonesia from his herbarium was either collected by others or from from cultivated material.
