Samples of approximately 500 mg of dried leaves were extracted once in 70 mL of petroleum ether by refluxing for 1.0 h. This shortened procedure, modified from previous work (33), resulted in the extraction of 95-98% of the artemisinin and its precursors artemisinic acid and dihydroartemisinic acid from the samples, as verified by a second extraction of three random samples. The supernatant was transferred to 150 mL glass beakers and evaporated to dryness in a hood. The following day, beakers were washed twice (10 mL each wash) with acetonitrile and filtered through a PTFE or nylon filter (0.45 ím) attached to a 5 mL syringe. These two washes were performed by rubbing acetonitrile on the sides and bottom of the beaker with a stainless steel spatula and by vortexing each wash around the tilted beaker. Recoveries for artemisinin and precursors were 95-97% with the first 10 mL wash, with the remaining being recovered in the second 10 mL wash. The samples were transferred to high-performance liquid chromatography (HPLC) flasks and analyzed in the same day that they were evaporated to dryness and reconstituted in acetonitrile. However, because the hood where samples were evaporated was not in total darkness and dihydroartemisinic acid photooxidizes to artemisinin under light, the dihydroartemisinin levels reported in this work were probably lower than the levels found in plants at the moment of sampling.