Peter Thonning was a Danish physician and botanist.
He was sent to Ghana by the Danish government to supervise the plantations of that colony, and he lived there from 1799 to 1803. His herbarium was destroyed during the shelling of Copenhagen by the British in 1807. Only the duplicates and manuscripts in the possession of Heinrich Christian Friedrich Schumacher survived. Today, around 1,050 samples are preserved at the University of Copenhagen Botanical Garden.
The genus Thonningia of parasitic plants was named after him by Martin Vahl. This botanist is denoted by the author abbreviation Thonn. when citing a botanical name.