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. On January 10, 1953, he married the botanist Isa Irmgard Hansen, whom he met in Berlin in 1952. They collected plants together in the Hawaiian archipelago. After 1956 Isa Degener was a coauthor for Flora Hawaiiensis.[3][4][5]Amy B. H. Greenwell assisted in some of the volumes, and left her property as a botanical garden.[6]
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.[2]
Degener was guest botanist on the second Cheng Ho expedition, which lasted from 1940 to 1941 and was sponsored by Anne Mills Archbold. During about eight months he collected over 2,000 specimens from Fijian plants, which were sent to Albert Charles Smith and other specialists in the United States. In 1949 Degener published a book describing his travels and experiences in the Fiji Islands.[7]
The tree Degeneria vitiensis, which he discovered in Fiji in 1941, is named after him. He died January 16, 1988, in Honolulu, Hawaii.
They were commended by the Hawaiian Senate for their conservation work.[3] Many of the plants collected by Otto Degener belong to species that are now extinct.[9]
^Mill, Susan W.; Wagner, Warren L.; Herbst, Derral R. (May 1985). "Bibliography of Otto and Isa Degeners' Hawaiian floras". Taxon. 34 (2): 229–259. doi:10.2307/1221781. ISSN0040-0262. JSTOR1221781; published online 2019{{cite journal}}: CS1 maint: postscript (link)
^Raup, H. M. (1950). "Review: Naturalist's South Pacific Expedition: Fiji by Otto Degener". The Quarterly Review of Biology. 25 (2): 204. doi:10.1086/397552. ISSN0033-5770. The review refers to "Mrs. Anne Archbold" — this is wrong — she divorced Armar Dayrolles Saunderson in 1922 — her name was never "Mrs. Archbold".