Diadelphous condition of stamens is found in
Diadelphous androecium is defined by filaments united into two bundles while anthers remain free. In Papilionoideae of Fabaceae, exemplified by Pisum sativum, nine stamens fuse into a sheath enclosing the ovary and one posterior stamen stays free, formula (9)+1. This arrangement protects nectar at base and guides bee foraging, keel petals must be depressed. China rose shows monadelphous tube, sunflower syngenesious where anthers unite, mustard tetradynamous 4+2 free. Diadelphous therefore reliably separates pea from other families and reflects papilionaceous floral architecture linked to legum
Ref: NCERT Class 11 Biology, Chapter 5: Androecium types diadelphous; Kochhar, Plant Systematics, Fabaceae
