<p>Animal-plant interaction processes are essential for the maintaining of ecosystem services, such as seed dispersal, a critical mechanism in the establishment and dynamics of populations of botanical species in tropical forests. Large frugivorous birds, such as guans, are key players in this process, dispersing seeds of various plant species in the Atlantic Forest. The study presents and analyzes botanical species as part of the diet of the dusky-legged guan (jacuguaçu—<i>Penelope obscura</i>) with evidence of 294 records of species consumed, in different regions and states of Brazil, belonging to 60 families and 212 species. The consumed items were essentially fruits, but there are also records of leaves, flowers and seeds. Of the fruits, the most consumed is the juçara palm (<i>Euterpe edulis</i>), a key species of ecological and socio-economic importance for the Atlantic Forest. Of all the fruits consumed, 85% were ingested whole, which characterizes the species as an endozoochoric disperser. We draw attention to the peculiar consumption of leaves, by adults and juveniles, of 14 plant species, several with recognized human medicinal potential. We also highlight the use of fruits of exotic species, 23% of the total. The dusky-legged guan is a species potentially dispersing and sowing seeds, very sensitive to deforestation, with a high functional potential that contributes to the dynamics and maintenance of Atlantic Forest fragments, as well as to the development and establishment the dynamics of forest restoration by dispersing and facilitating the germination of native species, mainly species of the functional diversity group.</p>