Developmental studies of Artemisia annua: flowering and artemisinin production under greenhouse and field conditions.

Cuttings of a clone of A. annua L. (Asteraceae), grown under 16 h photoperiod for 55 days were transferred to six photoperiod treatments in the greenhouse. Under short photoperiods (8, 10, or 12 h), plants flowered after two weeks; plants under long photoperiods (16, 20, or 24 h) remained vegetative until termination of treatment after 10 weeks. When plants grown under long photoperiod treatments were transferred to 8-h photoperiod, flowering occurred 2 weeks later. Flower induction in plants grown under field conditions occurred when the photoperiod was determined to the 13.3 h. Artemisinin levels in all studies were found to be highest at anthesis. Artemisinin content was 4- to 11-fold higher in inflorescences than in leaves.