Arvo Jaakko Juhani Jalas (7 May 1920 – 1 December 1999) was a Finnish botanist.
[1] After the war, he completed his PhD in Botany in 1950, with a dissertation entitled Zur Kausalanalyse der Verbreitung einiger nordischen Os- und Sandpflanzen[2] on the distribution, ecology and sociology of the plants of eskers and sandy areas of northern Europe.
He was regional adviser for Finland to the Flora Europaea project, and became co-chairman of the mapping project for European vascular plants Atlas Florae Europaeae.
[3] He was a founding member of OPTIMA (the Organization for the Phyto-Taxonomic Investigation of the Mediterranean Area).
He was also specialised in the study of Caryophyllaceae and the genus Thymus, a matter which occupied a long period of his professional life.