Floral development insights into two species of Erythrina (Fabaceae: Papilionoideae: Phaseoleae) pollinated by hummingbirds and passerines

Erythrina is a Pantropical bird-pollinated genus of Fabaceae. Thus, its flowers are usually large, showy, red, or yellowish, which offer nectar as a floral resource. There are two main interaction systems with birds: in one, the inflorescences are erect, and the flowers are horizontal, offering no landing platform; in the other, the inflorescences are horizontal, and the flowers parts are more exposed. Despite their structural variation, little is known about how species of the same genus diverge ontogenetically to form functionally different flowers. Therefore, this study aimed to investigate floral development in two species according to their pollination system. Erythrina speciosa is pollinated by hummingbirds, and E. poeppigiana is pollinated by passerines. Flowers and buds were collected and fixed for analysis using scanning electron microscopy and light microscopy. Some characteristics are common to both species: the formation of a pseudoracemose inflorescence, the unidirectional emergence of floral organs, and the formation of a short staminal tube involving nine of the ten stamens (androecium diadelphous). Other characteristics, notably those related to the late stages of floral development, gradually diverged. Among them are inflorescence formation pattern; the formation of reduced and free keel petals in E. speciosa , while in E. poeppigiana they are longer and merge; and the participation of the standard in the floral display. Such characteristics may not be phylogenetically related and reveal the potential ontogenetic pathways of functional convergence that flowers have experienced throughout evolution in Erythrina .