Floral development of one of the oldest dioecious lineages of Arecaceae reveals different stages of dicliny in pistillate and staminate flowers

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.