Floral development in Melaleuca and Callistemon (Myrtaceae)

Floral development of seven species of Melaleuca and four species of Callis temon is compared. The multistaminate fascicles of Melaleuca develop from s tamen primordia initiated on antepetalous pre-staminal bulges (PSBs); the r esultant bundles of stamens become separated by hypanthial expansion as the flower bud enlarges. In most species of Callistemon examined the stamen pr imordia are initiated directly on the floral apex, and the stamens are dist ributed evenly around the hypanthium at anthesis. The possession of large a nd prominent PSBs, and thus stamen fascicles, is a feature of most species of Melaleuca and their total absence is a feature of most species of Callis temon; however, there is a continuum between these two extremes; Several ta xa of both genera exhibit intermediate morphology. In C. glaucus (Bonpl.) S weet, small but distinct PSBs develop, which influence antepetalous stamen groups that remain contiguous at anthesis. This also occurred in M. leucade ndra (L.) L. This variable expression of PSBs is the result of differences in the timing of stamen initiation. Other variable features are determined by the space available for primordium initiation and the patterns of growth and expansion of the developing flower.