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Arecaceae subtribe Mauritiinae are a lineage of Neotropical dioecious species in subfamily Calamoideae, the earliest diverging and most diverse group of palms regarding sexual systems. Ontogenetic and anatomical studies of reproductive structures contribute to the understanding of evolutionary relationships, but there is a lack of detailed information. We describe the anatomical floral development of Lepidocaryum tenue, Mauritia flexuosa and Mauritiella armata (subtribe Mauritiinae) using standard light microscopy techniques. Three central moments in the development of pistillate and staminate flowers were identified: the initial phase of development of the floral meristem; the phase of determination of the whorls that will compose the pistillate and staminate flowers; and the phase of differentiation (pre-anthesis) of these whorls. Although the pre-anthetic flowers are diclinous, they are initially monoclinous, suggesting a hermaphrodite ancestor for Mauritiinae. The development is asynchronous since, in pre-anthesis, the pistillate flowers have staminodes that produce non-viable pollen grains, whereas the staminate flowers do not even have a pistillode. Staminodes may have a secondary function in attracting floral visitors.

Amorimia (Malpighiaceae) was recently segregated from the polyphyletic Mascagnia and placed in the malpighioid clade; identifying new characters based on leaf structure is among the first steps towards a proper generic delimitation of these segregates of Mascagnia. A comprehensive study describing and testing the relevance of leaf-structure characters in the evolution of Amorimia and related Neotropical genera is presented. We sampled all 15 Amorimia spp. and, as outgroups, eight species from the closely related Neotropical genera (Diplopterys, Ectopopterys, Mascagnia, Peixotoa and Stigmaphyllon). We scored 85 structural characters and mapped them on the most recent phylogenetic tree recovered for the genera. The presence of druses in the palisade parenchyma, the position of fibres alongside the vascular bundle and the occurrence of fibre blocks near the margin of the leaf blade were recovered as anatomical synapomorphies for Amorimia. Our results are a first step towards recovering anatomical and macromorphological synapomorphies for newly identified lineages of Malpighiaceae, such as Amorimia.