The genus Theobroma has two economically important species: cupuaçu (Theobroma grandiflorum) and cacao (Theobroma cacao). There are other species of the genus such as the cupuí (T subincanumi) also native to the Amazon, which can contribute important genes for the improvement of these two species. The transfer of genes between species can be done through hybridization, and the knowledge of the reproductive biology of cupuí can provide subsidies for its hybridization with cupuaçu and/or cocoa. In the present work the floral behavior of cupuí was studied. The studies were carried out in the Experimental Station of Genetic Resources "José Haroldo" in Benevides-PA, using 6 plants from the collection "Basil Bartley" whose flowers were observed at 6 am, 10 am, 2 pm, 6 pm and 10 pm for 4 consecutive days. Sepals begin their rupture both at the apex and base, occurring most frequently at 10 pm (45.4% of the floral buds). Anthesis occurs most frequently at 10 pm the next day (21% of floral buds) and abscission between 2 and 6 am the next day (21%). The time that the flower remains on the plant is 24 hours. The cupuí flower has an almost imperceptible odor to the human sense of smell, although it can be better perceived between 10 am and 2 pm on the day of anthesis. The stigmatic arms are of the "dry" type. The ignules along with the cogenules are the parts of the flower that have the most intense odor. The receptivity period accessed indirectly by the reaction with Hydrogen Peroxide suggests that cupuí flowers are most receptive between 10 am and 2 pm on the day of anthesis. Cupuí showed a natural pollination rate of 8.3% with "more than 60" pollen grains, generally arranged in clusters and preferentially deposited on the median portion of the stigmatic arms. The flowers showed different behavior among individuals.
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