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Leaf ontogenesis is imperative for the establishment and regulation of its structural and functional properties, in addition to being an excellent tool for assigning specimens to different groups of angiosperms. Even though the importance of leaf morphology and anatomy for taxonomic use is well known, few studies have addressed the processes of leaf ontogeny in Melastomataceae. Herein, we sought to define the ontogenetic steps of leaves of Trembleya phlogiformis DC., highlighting the indumentum, to understand the main functional traits. Shoot apex, young, and fully expanded leaves were processed by typical light microscopy procedures. At the first node, leaf primordia are densely covered with trichomes and emergences. The adaxial layer of ground meristem gives rise to the palisade parenchyma, the procambium originates from median layers of ground meristem, and the spongy parenchyma develops from abaxial layers of ground meristem. The differentiation of isobilateral mesophyll on leaves of T. phlogiformis, a common feature in Microlicieae, comes from ground meristem stratification. However, T. phlogiformis stands out by showing cells with irregular shapes in the leaf mature spongy parenchyma. The leaf ontogeny reveals distinct mechanisms of cell differentiation and may be important for the establishment of functional adaptive traits.