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The Developmental Basis of Diverse Carpel Orientations in Grevilleoideae (Proteaceae)

1996; University of Chicago Press; Volume: 157; Issue: 4 Linguagem: Inglês

10.1086/297355

1537-5315

Andrew W. Douglas, Shirley C. Tucker,

Plant Reproductive Biology

We examined and compared floral and inflorescence ontogenies among taxa in Proteaceae, primarily of the subfamily Grevilleoideae, to define the developmental events responsible for diverse orientations of the single carpel. Among the 29 genera and 39 species investigated, six orientations of the carpel are observed that can be divided into two larger groups of three: the tepal-bisecting group, in which the median sagittal plane of the carpel bisects a tepal, is defined on the basis of the tepal they bisect relative to the floral axis (adaxial, abaxial, and lateri-axial); the diagonal group, in which the median sagittal plane of the carpel bisects the point of intersection between two of the four valvate tepals, is defined by the two tepals that the ventral side of the carpel plane would bisect. There is an apparent conservation of specific carpel orientations and developmental processes that result in some of the carpel orientations among some of the taxa. The carpel orientations in Macadamia and Floydia are variable between the lateri-axial and the adaxial/lateral diagonal condition. Developmentally, the orientation of the carpel is usually associated with the amount of meristematic space available after stamen initiation: in most cases, the cleft of the carpel develops in a plane perpendicular to the longer diameter of the remaining floral apex. Two major developmental differences among the taxa included the lateral and terminal inception of the carpel primordium, an apical residuum being apparent in flowers of the former. In taxa of Banksiinae, Lambertiinae, Cardwelliinae, and Gevuininae, the floral meristem, after stamen initiation, shows differential growth before the differentiation of a carpel that is specific to each subtribe. These results clarify homologous conditions of carpel orientation and floral symmetry in Proteaceae that will prove useful in delimiting natural groups within the family as well as provide the starting point for a developmental analysis of morphological transformation and symmetries in proteaceous flowers.