The genus Commelina includes weed species of difficult control in several crops, chiefly when the herbicide glyphosate is used repeatedly. This work was conducted to evaluate the differences between the anatomic features of Commelina benghalensis and Commelina diffusa, grown under sun and shade conditions, which could influence herbicide absorption and translocation. The stomatal apparatus of the two species is similar and the leaf is amphistomatic. C. diffusa has a greater number of stomata in relation to C. benghalensis. The number of stomatas in the leaf epiderm is greater in C. diffusa (38/mm²) than in C. benghalensis (33.66/mm²), in the abaxial (54.86/mm²) rather than in the adaxial epiderm (16.80/mm²) and under sun (37.89/mm²) rather than shade conditions (33.77/mm²). The abaxial epiderm has a greater number of stomata under sun conditions. Similar secretory hair is present in both species, but in greater number in C. diffusa. Only C. benghalensis presented tector hair: (i) long with slender extremity and (ii) short with curved extremity. Long hair is concentrated in the abaxial epiderm and short hair in the adaxial epiderm. Although the presence of hair in the leaf epiderm is frequently associated to greater herbicide absorption, it is believed that the determinant factor of greater susceptibility of C. benghalensis to glyphosate in comparison to C. diffusa could be related to the starch stock of the stem. While C. benghalensis presents fewer and smaller starch grains in the pith parenchyma, C. diffusa presents larger and numerous starch grains, which may make herbicide simplastic translocation slower, reducing the herbicide accumulated in the growth points, and allowing it to regrowth even after total leaves loss.
C. diffusa; C. benghalensis; chemical control
