LYNCH, STEVEN P.1*, LINDA E. WATSON2, PETER MEYER1, BRIAN FARRELL3, and RICHARD OLMSTEAD4. 1Louisiana State University-Shreveport, LA 71115 USA; 2Miami University, Oxford, OH 45056 USA; 3Harvard University, Cambridge, MA 02138 USA; 4University of Washington, Seattle, WA 98195 USA. - Molecular phylogeny of North American Asclepias (Asclepiadaceae).
The diverse floral morphology in the Asclepiadaceae historically has
created taxonomic confusion in the family, especially at the generic
level. In 1954, Robert Woodson sank 20 North American genera into
synonomy under Asclepias, creating nine subgenera and an
additional eight series under the largest subgenus, Asclepias.
To clarify relationships within the genus of approximately 114
species, we have phylogenetically analyzed ITS nucleotide sequences
for 76 Asclepias species, representing all of Woodson's
subgenera and series. The data set of 152 phylogenetically-informative
characters supports the monophyly of Asclepias. A basal clade
is present, composed of species from Series Incarnatae. All
remaining species occur in its sister clade, which has little
resolution within it. Thus, it appears that there are two major
lineages within Asclepias, one defined by erect pedicels and
cup-shaped stipitate hoods (e.g., Series Incarnatae,) while the
other clade contains species with reflexed pedicels (with few
exceptions) and more variable hood morphology.
Key words: Apocynaceae, Asclepias, Asclepidaceae, ITS, phylogeny