| Fredrik Børgesen | |
| Birth Name: | Fredrik Christian Emil Børgesen |
| Birth Date: | 1 January 1866 |
| Birth Place: | Copenhagen, Denmark |
| Death Place: | Frederiksberg, Denmark |
| Nationality: | Danish |
| Fields: | Botany pscyhology |
| Workplaces: | University of Copenhagen |
| Alma Mater: | University of Copenhagen |
Fredrik Christian Emil Børgesen (1 January 1866 in Copenhagen – 22 March 1956 in Frederiksberg) was a Danish botanist and phycologist. He graduated in botany from the University of Copenhagen and was subsequently employed as an assistant at the Botanical Museum (1893–1900). His doctoral thesis dealt with the marine algae of the Faroe Islands (1904). Later, he became librarian at the Library of the Botanical Garden (1900–1935).
Børgesen made investigations of marine algae e.g. around India, Mauritius, the Canary Islands and the Antilles.
Many species have been named to his honour, e.g. Coccoloba borgesenii (Polygonaceae) and numerous algae, e.g. Hypnea boergesenii (Hypneaceae) and Padina boergesenii (Phaeophyceae).
The work is a result of studies conducted during the expedition to Venezuela and the Antilles organized by Eugen Warming 1891–1892. The whole work has a distinct "Warmingian" appearance, organized as it is according to major vegetation types (halophytic vegetation, psammophytic vegetation, etc.) and with descriptions (incl. line drawings) of leaf and stem morphology in relation to habitat. Børgesen and Paulsen were students of Eugen Warming. Later, the both went their own ways, mainly to phycology and marine biology.
These three papers were later reprinted in one volume:[2]
See also: History of phycology.