Dr. Friedrich Ludwig Emil Diels (24 September 1874 – 30 November 1945), was a German botanist.
Diels was born in Hamburg, the son of the classical scholar Hermann Alexander Diels. From 1900 to 1902 he traveled together with Ernst Georg Pritzel through South Africa, Java, Australia and New Zealand.
Shortly before the first world war he travelled New Guinea and in the 1930s in Ecuador. Especially his collections of plants from Australia and Ecuador, which contained numerous holotypes, enriched the knowledge of the concerning floras. His monography on the Droseraceae from 1906 is still a standard.
The majority of his collections were stored at the botanical garden in Berlin-Dahlem, whose vicedirector he had been since 1913, becoming its director in 1921 until 1945. His collections were destroyed there during an air raid in 1943. He died in Berlin on the 30th of November 1945.
- J.S. Beard in -Beard, J. S. (John Stanley) (1990), Plant life of Western Australia, Kangaroo Press, ISBN 978-0-86417-279-2 – page 9 – emphasises the book – Diels, Ludwig (1906), Die pflanzenwelt von West-Australien südlich des wendekreises : mit einer einleitung über die pflanzenwelt Gesamt-Australiens in grundzügen, Verlag Von Wilhelm Engelmann, retrieved 20 June 2012 was the first of its kind for Western Australia
- "MUELLER BOTANIC SOCIETY". The West Australian. Perth: National Library of Australia. 22 July 1902. p. 3. Retrieved 20 June 2012.
- IPNI. Diels.