The floral formula of Fabaceae shows which aestivation?
Fabaceae corolla exhibits descending imbricate or vexillary aestivation where posterior largest petal standard overlaps two lateral wings which in turn overlap two fused anterior keel petals enclosing diadelphous androecium and monocarpellary ovary. This papilionaceous arrangement protects sexual organs and guides pollinator landing, keel depresses to expose stamens. Valvate petals touch without overlap as in Solanaceae, imbricate multidirectional in Cassia, twisted regular overlapping in Hibiscus. Vexillary aestivation is synapomorphy for Faboideae subfamily Papilionoideae and central to pea floral formula ⚥ K(5) C1+2+(2) A(9)+1 G1 with marginal placentation.
Ref: NCERT Class 11 Biology, Fabaceae vexillary aestivation; Starr & Taggart, Papilionoideae floral diagram