Bloemontogenetische patronen in de Ericales sensu lato

The Ericales sensu lato are a morphologically very diverse order of the angiosperms. They represent one of the early diverging lineages of the asterids. Currently, about 25 families are recognised, which sometimes belonged to very distant groups in the past. In this work, we attempt to give an overview of the floral morphological and floral ontogenetic diversity within the order. We describe a number of developmental patterns and try to reveal evolutionary links that may support the phylogenetic hypotheses for the group. At the same time, we make a detailed study of floral characters and aim at accurate and refined circumscriptions of character states. In general, the flowers of Ericales are tetramerous or pentamerous, actinomorphic, and often bisexual. The persistent calyx usually develops spirally or sepals arise simultaneously or following a decussate pattern. Petals normally develop simultaneously and will fuse to form a sympetalous corolla. Stamens often become connate as well and they show a strong connection with the corolla. In the primuloid clade, where petals and stamens develop from common primordia, we use the term synstapetaly. We consider a diplostemonous organisation of the androecium to be the ancestral state within the order. An obdiplostemonous arrangement of the stamens is always due to secondary growth processes, except when one of the whorls is staminodial. Polyandry in Ericales results from different developmental patterns, so we assume an independent origin in several multistaminate taxa. The coenocarpous gynoecium consists of a superior or (semi-)inferior, incompletely septate ovary, a hollow, sometimes branched style, and an inconspicuous, capitate or merely lobed stigma. Placentation is basically axillary, and we demonstrate how all other occurring forms (apical, (sub)basal, free central and parietal) may be derived from an axillary condition. There are few to numerous anatropous, bitegmic or unitegmic, tenuinucellate ovules. Shifts from a bitegmic to a unitegmic condition did occur in several lineages, sometimes with transitional forms still present. Certain groups possess floral nectaries, which are then most commonly associated with the gynoecium. Specific and typical adaptations of the floral structure and floral characteristics are usually linked to aspects of pollination, and we discuss a few examples. Our results support the recognition of several clades within the Ericales, e.g. the primuloids, which are the core group of