Systematics Section / ASPT
Ionta, Gretchen M. , Judd, W. S. .
Phylogenetic relationships and character evolution in Periplocoideae (Apocynaceae).
PERIPLOCOIDEAE, a subfamily of Apocynaceae s.l. occurring in the Old World tropics and sub-tropics, has long been recognized as a distinct group based on the presence of unique scoop-shaped translators (hardened secretions of the stylar head), upon which pollen is shed as tetrads or pollinia. The small size of this group belies its importance in the taxonomic history of Apocynaceae s.l.: until recently, the flowers of Periplocoideae have been regarded as transitional between the simpler forms found in Apocynaceae s.s. and the highly synorganized flowers of Secamonoideae and Asclepiadoideae, thus the group was treated either as a subfamily of Asclepiadaceae, or as a separate family, Periplocaceae. Recent phylogenies based on molecular and morphological data, however, showed Periplocoideae to be nested within "Apocynoideae", and today a more inclusive Apocynaceae s.l. is recognized. It follows that the complex floral forms found in Periplocoideae and in the Secamonoideae + Asclepiadoideae clade (and lacking in the rest of the family) evolved separately, thus the homology of these traits must be reconsidered. For this study, we utilized morphological data and sequences obtained from chloroplast and nrITS DNA in a cladistic analysis of Periplocoideae. The resulting phylogeny allowed us to infer relationships within the subfamily and provided a framework that we subsequently used to explore patterns of character evolution in Periplocoideae, focusing on the transition from pollen tetrads to pollinia. Pollinia are restricted to Orchidaceae and three subfamilies of Apocynaceae: Periplocoideae, Secamonoideae, and Asclepiadoideae. Our results confirmed the hypothesis set forth by other researchers, that pollinia most likely evolved separately in the Periplocoideae and in the Secamonoideae + Asclepiadoideae clade, and indicated multiple origins of this complex morphological trait within Periplocoideae alone.
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1 - University of Florida, Department of Botany, 220 Bartram Hall, P.O. Box 118526, Gainesville, Florida, 32611-8526, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Wednesday, August 2nd, 2006
Time: 11:15 AM