Paul Runar Collander (1 May 1894 Vyborg – 25 May 1973 Helsinki) was a Finnish botanist.
He was an adjunct professor of plant physiology at the University of Helsinki from 1935 to 1939, and professor of botany from 1939 to 1961.
[1] He gained international acclaim for his research on the effect of molecular size and solubility ratios on the ability of substances to penetrate the cell membrane.
[2] He presented the "lipoid filter theory" of permeability and further developed it.
Collander also wrote several works on the history of botany.