Morphological and Histological Evaluations of Flower Development in Elliottia Racemosa

Elliottia racemosa is a rare, woody species restricted to Georgia’s coastal plain. Seed set can be low or nonexistent and no sexual recruitment has been observed in the wild. Our previous work shows that stigmatic receptivity in Elliottia racemosa is not optimal for pollen germination and tube growth until flowers are fully open and petals are abscising. Stigmas are non-papillate and develop a raised and textured central surface surrounding a clefted opening to a stylar canal. The objective of this study was to evaluate stigma and stylar development throughout seven defined stages of floral development ranging from small unopen buds to flowers with abscised petals.  In early stages, the style is solid and stylar canal formation occurs in later stages. Exudate is secreted into a clefted region of the stigma where pollen is captured, and facilitates germination and tube growth through the hollow canal. Stylar canal structure and development was observed, and the mode of exudate formation and secretion discerned.  Histochemical staining was conducted to visualize structures and characterize stigmatic exudates and stylar secretions, i.e., to detect the presence of a cuticle (Auramine O), polysaccharides (Periodic acid-Schiff), proteins (Coomassie blue), and lipids (Sudan black).