Lamina size, thickness, venation, and anatomy are studied in 15 species of Heliconia (Heliconiaceae), 3 species of Musa, and 1 of Ensete (Musaceae). The most typical laminas of these genera are large and oblong and have an acute or irregular apex and an asymmetrical cordate base. The laminar veins are parallel and are oriented essentially perpendicular to the costa and the margin. However, there is considerable variation in lamina architecture in the Heliconiaceae. Thickness ranges considerably across the lamina, with considerable variation between species. The only pattern common to all species is that the blades are thinner at the margin than at the costa. The veins of the lamina occur in a number of size classes that are arranged into a repeating unit called a set. Set patterns are described for the species and families. Although the Heliconiaceae and Musaceae do not differ in general set pattern, variation in the Heliconiaceae tends toward simpler sets, whereas the Musaceae tends towards more complex sets. Lamina anatomy is similar to that reported in the literature for these families, with several notable exceptions. The Heliconiaceae and Musaceae may be distinguished by characteristics of their lamina anatomy and by the fact that Musaceae blades have an irregular apex. The value of these characters for taxonomic and cladistic analyses is discussed. Key words: leaves, plant anatomy, vasculature, Zingiberales, Musaceae, Heliconiaceae.