Otto Degener (May 13, 1899 – January 16, 1988) was a botanist and conservationist who specialized in identifying plants of the Hawaiian Islands.
Degener was born May 13, 1899 in East Orange, New Jersey. Degener graduated from the Massachusetts Agricultural College (now University of Massachusetts Amherst). Intending to spend a year as a tourist, he arrived in Hawaii but decided to stay. He received his MA from the University of Hawaii in 1922 and his PhD from Columbia University. He taught Botany at the University of Hawaii from 1925 to 1927, and was the first naturalist for what are now Hawaii Volcanoes National Park and Haleakala National Park.
In 1932, Degener started the first book on Hawaiian plants published since that of William Hillebrand in 1888. It was titled Flora Hawaiiensis, and published in several volumes over his lifetime. Amy B. H. Greenwell assisted in some of the volumes, and left her property as a botanical garden. He collected over 36,000 different species and preserved some 900 threatened and endangered plants. His specimens were left to the New York Botanical Garden.
The tree Degeneria vitiensis, which he discovered in Fiji in 1942, is named after him. He died January 16, 1988 in Honolulu, Hawaii.