We evaluated the ontogeny of the understory shrub Psychotria tenuinervis Müll.Arg., considering morphological and morphometric characters. Four ontogenetic stages were identified: seedling, juvenile, immature and adult (vegetative and reproductive phases). Size measurements and allometric relationships of the stem and crown were compared between the immature and adult stages. Diameter and total height of the stem, as well as crown depth and width, increased throughout the ontogenetic stages and differed among immature, vegetative adult and reproductive adult individuals. The number of branches was lower in immature individuals than in vegetative and reproductive adult individuals but did not differ between the last two. The bifurcation ratio did not vary during ontogenetic development. In general, allometric relationships between the stem and the crown were similar among the ontogenetic stages. Although there was a progressive increase in size during ontogenetic development, there was no change in the allometric relationships between the size variables and architecture of P. tenuinervis, indicating that the form of individuals does not change over the course of ontogeny.730736Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)