Floral Ontogeny of Pelargonium × domesticum

Abstract

Floral ontogeny of Pelargonium xdomesticum was examined for two cultivars grown under identical environmental conditions. Apical meristems of `Duchess' and `Jennifer' were vegetative at the commencement of the experiment. Meristems were examined every five days over an experimental period lasting 85 days. Floral ontogeny was the same for both cultivars, although the timing of floral initiation of the meristem, floral organ initiation, and floral organ development differed. The vegetative meristem was convex with leaf primordia initiated on either side in an alternate pattern. Early floral initiation was characterized by formation of a cleft towards one side of the meristem, followed quickly by a second cleft on the other side. Between the clefts new meristems developed. New meristems lacked leaf primordia. Proliferation of meristems continued until numerous meristems were organized in a cluster arrangement at the apex of the shoot. Proliferation of meristems at the apex continued until multiple inflorescences had developed. Inflorescences were subtended by bracts. Floral organ primordia were initiated in a succession of four whorls: sepals, petals, androecia and gynoecium. Petals and androecia appeared to develop simultaneously soon after sepal primordia were visible. Petal primordia remained small while the androecia continued to grow. The gynoecium first formed a conical shape, with carpels protruding from the base in a bulbous fashion. At the distal end of the gynoecium, divisions appeared which developed into stigmatic lobes. As the gynoecium elongated, stigmatic lobes became more pronounced. Petal elongation concurred in synchrony with elongation of the gynoecium. On one experimental unit of `Duchess' two florets had opened at 750 total cumulative moles. No `Jennifer' florets had opened by termination of the experiment.