Morphology, anatomy and ultrastructure of petals in Alicia anisopetala and Callaeum psilophyllum (Malpighiaceae): implications for pollinator attraction.

In Malpighiaceae species, the corolla consists of five petals, with the posterior petal, or flag petal, being distinct in shape and size. This differentiation facilitates the proper orientation and positioning of pollinators, allowing them to access floral oils while simultaneously contacting the anthers and the stigma, thereby enabling pollen transfer. To better understand the role of the corolla in pollinator attraction, a study was conducted on the morphology, anatomy and ultrastructure of all petals of Alicia anisopetala and Callaeum psilophyllum. Flowers at anthesis were collected and fixed for subsequent analysis. Light microscopy, scanning electron microscopy and transmission electron microscopy techniques were employed. The results revealed morphological and anatomical differences between the posterior and lateral petals of both species. Hairs, druse crystals, and fimbriae were identified along the petal margins. Ultrastructural analysis revealed metabolically active and secretory epidermal cells, associated to scent secretion, with distinctive characteristics observed in the emergent structures of the posterior petal of C. psilophyllum. In summary, this study provides detailed information on petal structure in these Malpighiaceae species, suggesting adaptations for pollinator attraction through specific morphological features and fragrance secretion. These findings contribute to a deeper understanding of the fundamental role of the corolla in the pollination of A. anisopetala and C. psilophyllum.