The objective of this study was to determine the effects of an ethanolic extract of Annona muricata, or Guanábana, applied for various exposure periods in concentrations of 25 µg/mL, 50 µg/mL and 100 µg/mL on the cell cycle of root meristems of the Roja Arequipeña variety of onion, Allium cepa. The twelve treatments of ethanolic extract of Annona muricata used to induce growth in the onion roots were as follows: T1: 0 µg/mL for 6 hours, T2: 25 µg/mL for 6 hours, T3: 50 µg/mL for 6 hours, T4: 100 µg/mL for 6 hours, T5: 0 µg/mL for 12 hours, T6: 25 µg/mL for 12 hours, T7: 50 µg/mL for 12 hours, T8: 100 µg/mL for 12 hours, T9:0 µg/mL for 24 hours, T10: 25 µg/mL for 24 hours, T11: 50 µg/mL for 24 hours and finally T12: 100 µg/mL for 24 hours. After exposing the roots to the treatment, the cells were mounted on slides, stained, and examined microscopically. Results of microsc...