This study investigates the floral morphology and development of two legume species from the subfamily Caesalpinioideae, Biancaea decapetala (a caesalpinioid), and Albizia julibrissin (a mimosoid), using scanning electron microscopy. The floral organ initiation in A. julibrissin involved the helical orientation of sepals’ formation, simultaneous initiation of petals, and formation of the ring meristem in place of stamens. Whereas in B. decapetala, organ whorls grow unidirectionally, from abaxial to adaxial, a characteristic found in the subfamily Papilionoideae. However, the floral development sequence in B. decapetala differs from papilionaceous flowers, as it lacks petal specialization and features a fused staminal tube. While fused sepal tube, free stamens, and short style were observed in flowers of B. decapetala; fused petals, fused staminal tube, and long style occurred in flowers of A. julibrissin. The petal aestivation is valvate in A. julibrissin, compared to ascending cochleate in B. decapetala. The observations during the initiation and developmental stages of floral whorls are essential to unravel the functional specificity of appendages. A. julibrissin belongs to the Mimosoid clade, which was until recently placed outside the Caesalpinioideae subfamily (of which B. decapetala was always been a part of) due to its floral architecture. There has been significant number of discussions and deliberations in the botanical community about the placement of this clade in the subfamily. Understanding of floral development in the subfamily and comparison of caesalpinioids with mimosoids can be crucial in evaluating the phylogenetic placement of the mimosoid clade. While most changes in the developmental sequence may appear subtle and minute, these are imperative for the remarkable disparity in the floral morphology of legumes.