The Myrtaceae family is clearly predominant in tropical and subtropical regions of the world. In the Amazon several genera occur, Myrcia and Eugenia being the most common. The present work aims to establish a practical morphological concept about the two genera, emphasizing the types of inflorescences that characterize them; to discuss the relationships among Calyptranthes, Marlieria and Myrcia. For this study, exsiccates from the MG and IAN herbaria were analyzed under a stereomicroscope, following the classical procedures used in plant taxonomy. Thirty-five Myrcia and 47 Eugenia species were analyzed. Due to the large number of samples analyzed, the types of inflorescences and floral morphology were further detailed. Morphological characterization: 1. Myrcia - Inflorescence in panicles, sometimes tyrosoid, axillary or terminal, open flower bud, sepals 5, rarely 4, distinct, arising from the upper edge of the hypanthium, which may or may not extend over the ovary, petals usually 5; 2. Eugenia - Uniflora inflorescence (sometimes in decussate pairs), racemes or umbellatae (reduced main axis of the raceme), axillary, cauliflora or terminal, open flower bud, sepals 4, distinct and imbricate, free already in the flower bud, hypanthium little or not prolonged over the ovary, petals 4. The species of greater occurrence are: Myrcia bracteata DC, M. cuprea (Berg) Kiersk.,M.falulx (Rich.) DC. andM. sylvatica (G. Meyer) DC: E. biflora (L.) DC., E.flaoescens DC., E. muricata DC., E. patrisit Vahle E.punicifolia (Kunth) DC.The relationships among Calyptranthes, Marlieria and Myrcia were analyzed, because they are considered close genera by specialists, mainly by the type of inflorescence, but they are separated by the characters of the flower bud. The work consists of descriptions, identification key and illustrations.
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