Anisophylly can be defined as the unequal growth of two leaves in a pair from a single branch node. It occurs in several opposite-leafed taxa, even in those with apparently no phylogenetic proximity. We have intended here to classify and describe the anisophylly found in ten species of Melastomataceae from two genera, Leandra and Miconia, using morphometric data. We developed a method to quantify the level of anisophylly in these species, using a parameter called “Anisophylly Index” (AI), with values ranging from nearly 0 (isophyllous) to 1 (strongly anisophyllous). A comparison between the leaves from the erect and lateral branches of Leandra barbinervis showed that this species has incomplete lateral anisophylly; i.e., only the lateral branches are anisophyllous, and in these only the pairs positioned in a dorso-ventral position are unequal, while pairs positioned in a horizontal position are isophyllous. The lateral branches of all species showed incomplete anisophylly. There is no apparent relation between anisophylly levels and area of the leaves. Anisophylly seems to be related to an increase in the efficiency on light capture, and perhaps is controlled by auxins. Its occurrence does not imply a gain or a loss of photosynthetic area of the anisophyllous pair, when compared to the isophyllous pairs in the lateral branches because total leaf area is equal (Table 1). Since the incomplete lateral anisophylly found in Leandra and Miconia is a character whose expression may vary according to environmental conditions and also between different regions of the same plant, it can not be considered as a reliable taxonomic character.