Floral ontogeny in Calliandra angustifolia (Leguminosae: Mimosoideae: Ingeae) and its systematic implications

The floral ontogeny of Calliandra angustifolia, studied using SEM, shows striking differences compared with all other investigated Mimosoideae. The initiation of the sepals is unidirectional from an adaxial to abaxial position, which is a very rare character within Leguminosae. Aestivation of the calyx is cochlear descending, which is a new character within Ingeae. The synchronous initiation of the petals and their valvate aestivation are the only characters that are congruent with the other studied Mimosoideae. The initiation of the androeceum is helical, which has never been found within Mimosoideae. The early pistil development resembles that of Zapoteca, which was recently segregated from Calliandra, whereas the middle and late developmental stages differ clearly in formation of a sessile pistil without a gynophore and an expanded capitate stigma. The presented character combination is unique within Mimosoideae, and no parallels to the genus Zapoteca could be found.