Rudolph Arnold Maas Geesteranus

Rudolf Arnold Maas Geesteranus (20 January 1911 in The Hague – 18 May 2003 in Oegstgeest), was a Dutch mycologist whose work on both ascomycetes and basidiomycetes helped to refine fungal taxonomy over a career of nearly six decades.

Early life and education

Maas Geesteranus was born in The Hague, but spent his childhood (from infancy until age 18) in the Dutch East Indies, where his family emigrated shortly after his birth. Upon returning to the Netherlands in 1929, he completed secondary school in The Hague and enrolled at Leiden University to study biology. While still a student, he joined the staff of the Rijksherbarium (the National Herbarium of the Netherlands) as a volunteer assistant—a post that proved pivotal in launching his scientific career. In mid‑1939, at 28, he was promoted to assistant, becoming the sole mycologist on the herbarium staff at that time.