XVI International Botanical Congess

Variation in ploidy levels was related with anatomical modifications and net CO2 assimilation in five Opuntia species growing in the semiarid lands of Mexico. The ploidy level ranged from diploid (2n=2X=22) to octoploid (2n=8X=88). Ploidy levels showed a positive relation with cuticular thicknes, stomatal size, but not relation was found with stomatal density. The daily net CO2 assimilation was extremely higher in cultivated octoploid (1025 mmol m-2 d-1) than in wild octoploids, hexaploids and diploid Opuntias, in wich the values of daily net CO2 assimilation varies from 128 to 233 mmol m-2 d-1. However, net CO2 assimilation by day, that was higher in hexaploid and octoploid plants than in diploid and tetraploid plants.