New insights into pollen release and presentation in legumes: the case of Myroxylon peruiferum, a papilionoid with non-papilionaceous flowers.

The species-rich legume family displays diverse mechanisms for pollen presentation and release, including brush, piston, valvular, and explosive types, influenced by variations in floral architecture. Among papilionoids, a group characterized by flag-flowers, early-branching species often deviate from this typical pattern. This study investigates Myroxylon peruiferum L.f., an early-branching papilionoid legume native to the Brazilian Atlantic Forest, with non-papilionaceous flowers. Through detailed macromorphological, anatomical, histochemical, and ultrastructural analyses of floral organs, we reveal new insights into pollen release and presentation mechanisms in legumes. Pollen is released through an unusual process: the anther opens via an apical wide slit that gradually extends toward the base, releasing pollen in stages. Ducts in the sepals, petals, ovary, and anther secrete translucent oleoresin droplets that harden when released into the external environment. These serve multiple functions, including enhancing flower visibility, facilitating secondary pollen presentation by attaching pollen to the anther apex and petal tips, and acting as olfactory attractants due to their terpene content. M. peruiferum presents several unique traits not previously described in this subclade, including (a) oleoresin overflow through anther pores, (b) uncommon rimose anther dehiscence, and (c) a novel form of secondary pollen presentation via oleoresin drops. These findings provide important new insights into the reproductive strategy of this species and offer broader implications for legume biology.