Common primordia and the double-headed inflorescence in ‘Renova’ red clover (Trifolium pratense L.), a papilionoid legume

Double-headed inflorescences subtended by one pair of bracts were commonly observed on ‘Renova’ red clover grown under experimental conditions. The early ontogeny of these double-headed inflorescences was investigated using scanning electron microscopy. The inflorescence was initiated as an outgrowth of the vegetative apical meristem in the axil of the penultimate bract. This outgrowth (the inflorescence meristem) was elongated along an axis drawn between the stem centre and the bract. While still small and before floret initiation had begun, it became divided by a median furrow into two inflorescence meristems. These two inflorescence primordia then developed asynchronously and with mirror symmetry. The primordium proximal to the penultimate bract showed enhanced growth and initiated florets earlier than its counterpart. The other primordium enlarged and initiated florets only after the ultimate bract primordium had formed. The inflorescence apices were progressively reduced by the initiation of florets as hemispherical protuberances. These two remnant apices were each ellipsoidal in shape and their long axes were tilted relative to the flowering stem axis, such that they faced each other. Florets were initiated in elliptical whorls and their organogenesis was zygomorphic. At maturity, the mirror symmetrical pattern of development was not evident, and no vegetative tissue could be seen between the adjacent inflorescences.