Pieter Groenhart (February 21, 1894 – November 3, 1965) was a Dutch lichenologist known for his research into tropical Asian lichens.
Born in Ilpendam, he became a teacher in 1916 and taught in several local elementary schools.
He returned to teaching in Malang until 1940, when he was transferred to a Government school at present-day Bogor.
[1] In 1942, Groehnhart was imprisoned in an internment camp, where he stayed until his release in 1945.
After returning to the Netherlands, he continued his studies of lichens, becoming especially interested in the genus Cryptothecia.