Johannes Paulus Lotsy or Jan Paulus Lotsy (11 April 1867 – 17 November 1931) was a Dutch botanist, specializing in evolution and heredity. He promoted the idea of evolution being driven by hybridization.

Lotsy was born into a wealthy family in Dordrecht and went to study at the Wageningen Agricultural College where his teachers included Martinus Beijerinck and then at the Göttingen University (1886-1890) where he studied lichens for his doctorate. He then went to Johns Hopkins University (1891–1895) as a lecturer and also served as director of the herbarium. From 1896 to 1900 he was sent to Java to work on cinchona research. He returned after suffering from malaria and then taught at Leiden University (1904-1909), as a lecturer in Systematic Botany. He became director of the State Herbarium (Rijksherbarium) 1906–1909, then Secretary of the Hollandsche Maatschappij van Wetenschappen.^[1]

Lotsy founded the Association internationale des Botanistes and was editor of the Botanisches Centralblatt and the Progressus rei botanicae. He proposed a system of plant classification, based on phylogenetics. Lotsy argued for a major role of hybridization in evolution^[2][3] including claims for human evolution.^[4]

Lotsy died at Voorburg following a surgery.^[5]

India (1895–1900), the United States (1922), Australia and New Zealand (1925), South Africa (1926–27), and Egypt (1930). He also studied the flora of Italy and Switzerland.

Lotsy argued that the monocotyledons were diphyletic, with the Spadiciflorae being derived from the dicotyledons (specifically Piperales) and the remainder from a hypothetical ancestor, the Proranales. Hutchinson, who argued for a monophyletic origin, considered this improbable.^[6]

• Category:Taxa named by Johannes Paulus Lotsy