Career
He specialized in research of marine algae and subarctic vegetation. During his career he undertook many botanical trips throughout Iceland. His main works are:
The marine algae of Iceland.
Botanisk Tidsskrift 25: 378—380.
1902-1903.
The marine algae of East Greenland. Meddelelser om Grønland 30: 1-73.
1904.
The marine algal vegetation of Iceland. The Botany of Iceland, edited by L. Kolderup Rosenvinge & East. Warming, J. Frimodt, Copenhagen, and John Wheldon and Company, London.
Volume 1, Participant 1, pp. 1–186.
1912.
The diatom Navicula jonssonii Østrup is named for him.
