Developmental and Structural Section
Evans, Rodger C. , Dickinson, Timothy A. , Campbell, Christopher S. .
Comparative ontogenetic Data for a Molecular Phylogenetic Hypothesis: implications for the origin of Maloideae from "Spiraeoideae".
Phylogenetic analyses of molecular data place some members of polyphyletic “Spiraeoideae” (Gillenia, Kageneckia, Lindleya, and Vauquelinia) at the base of a well supported clade that includes all Maloideae (x=17). Most striking of these results is placement of Gillenia with x=9 as the other three have x=15 or 17. These results lead to a hypothesis concerning the polyploid origin of Maloideae from an ancestral Gillenia lineage. To investigate implications of this hypothesis we have compared floral development in Gillenia, Vauquelinia, and several Maloideae. Our results demonstrate that the earliest stages of floral development are similar in all taxa, particularly in the initiation of gynoecial units from a common primordium in the centre of the floral apex. Gillenia initiates a raised pad of cells, whereas Vauquelinia and Maloideae initiate a ring primordium. All taxa initiate individual gynoecial units by differential cell division atop their respective common primordia. As the gynoecium of each develops, at least the bases of gynoecial units remain connate through to maturity. Ovule initiation and development in Gillenia, Vauquelinia and most Maloideae is identical and results in a pair of collateral, anatropous, and apitropic ovules, each associated with a funicular obturator. Where the taxa differ is in the development, or lack of development, of an inferior ovary. Mature Gillenia flowers are perigynous as zonal growth does not extend below the developing gynoecium. Mature Vauquelinia and Maloideae, on the other hand, develop partially (Vauquelinia) to fully (most Maloideae) epigynous flowers as a result of zonal growth in a region that extends below both the gynoecium and hypanthium. Changes in the localization and duration of zonal growth thus appear to be responsible for the origin of epigynous flowers found in most Maloideae. These apparently minor changes in morphogenesis nevertheless have resulted in a shift from dry dehiscent fruits to fleshy pomes.
1 - Royal Ontario Museum, Centre for Biodiversity and Conservation Biology, Royal Ontario Museum 100 Queen's Park, Toronto, Ontario, M5S 2C6, Canada
2 - Acadia University, Biology, 24 University Avenue, Wolfville, Nova Scoti, B4P 2R6, Canada
3 - University of Maine, Department of Biological Sciences, Orono, Maine, 04473-5751, USA
Presentation Type: Paper
Location: Alpine A (Snowbird Center)
Date: Monday, August 2nd, 2004
Time: 9:15 AM