Letter from A. Hansen c. 1984. Report of 80th birthday celebration incl. photograph in Brit. Cact. Succ. J., 19(3): centre page newsletter xxi (2001). Obituary in Kakteen And. Sukk. 70(11): 337. 2019.
Comments
See Tephrocactus Study Group 12(3): 37, 42-48 (2006) where pseudonyms were used.