borrowed from Russian florigen, from flori-flori- + -gen-gen
The Russian term was apparently introduced by the Soviet Armenian plant physiologist Mixail Xristoforovič Čajlaxjan (1902-91) in an article published in 1936 in the Doklady Akademii Nauk SSSR/Comptes rendus de l'Académie des Sciences de l'URSS. An English version of the article, entitled "New facts in support of the hormonal theory of plant development," was published in vol. 13 (1936) of the Doklady, pp. 79-83.