Some aquatic plant species have caused great damage to hydroelectric power dams in Brazil, due to their great capacity of reproduction. Nineteen quantitative structural characters of leaf blades were used to differentiate Brachiaria mutica, Brachiaria subquadripara, Panicum repens, Eichhornia crassipes, Heteranthera reniformis, Typha subulata, and Enhydra anagallis. Leaf blade samples were collected, fixed in FAA 50, infiltrated in glycol metacrylate resin, cut transversally with 8 mm thickness, and stained with toluidine blue. Structural characters in vein and internerval regions were quantitatively evaluated (%) for adaxial and abaxial epidermis, vascular bundle, vascular bundle sheath, esclerenchyma, parenchyma, and spongy aerenchyma. Leaf thickness, stomata and trichome number were determined at the internerval region. The quantitative structural characters of the leaf were submitted to Clusters Analysis and Principal Components Analysis. Three groups were formed according to similarity levels: group 1 - B. mutica, B. subquadripara, and P. repens (Poaceae); group 2 - E. crassipes and H. reniformis (Pontederiaceae), and E. anagallis (Asteraceae); group 3 - only for T. subulata (Typhaceae). The structural characters with high discriminatory degree were: adaxial epidermis (internerval region); abaxial epidermis, vascular bundle, vascular bundle sheath, esclerenchyma and spongy aerenchyma (middle vein and internerval region); leaf thickness; and stomata number. The quantitative structural characters allowed the differentiation of these aquatic weed species during the vegetative period.
aquatic plant; infestation; leaf anatomy
