EVANS, RODGER C.1* and TIMOTHY A. DICKINSON2. 1Biology Department, Acadia University, Wolfville, NS, Canada, B0P 1X0; 2Center for Biodiversity & Conservation Biology, Royal Ontario Museum, Toronto, ON, Canada M5S 2C6. - How do studies of comparative ontogeny and morphology aid in elucidation of relationships within the Rosaceae?
Phylogenetic analyses of sequence data from numerous sources provide
support for two large groups within the Rosaceae; Rosoideae s.s. (x =
7 plus Alchemilla ) and Gillenia plus Maloideae s.l.
(traditional Maloideae plus Kageneckia, Lindleya, and
Vauquelinia). While there is support for various other smaller
clades, the relationships between those clades remains less clear.
Nitrogen-fixing genera of the traditional Rosoideae form a clade that
comprises taxa (Cercocarpus and Chamaebatia) with a
single pistil containing a single basally inserted ovule that is not
associated with an obturator. The Spiraeeae (Aruncus,
Holodiscus, and Spiraea) as delimited by molecular
analyses include taxa whose floral ontogeny and mature morphology are
quite similar with regards to having approximately five free pistils
whose ovaries enclose two to many terminally inserted ovules each of
which is associated with an obturator. Amygdaloideae, minus
Prunus, differ in their numbers of pistils (1 in
Prinsepia; 5 in Exochorda and Oemleria), ovary
connation (present in Exochorda), but have very similar ovule
morphologies with respect to number, position within the ovary, and
association with an obturator. Molecular evidence also points toward a
relationship between Adenostoma (Rosoideae or its own tribe
Adenostomateae), Chamaebatiaria and Sorbaria; the latter
two are traditionally placed in Spiraeoideae or tribe Sorbarieae.
Although these taxa vary with respect to pistil and ovule number (one
pistil and two ovules in Adenostoma vs. five pistils that are
basally connate and multiple ovules in Chamaebatiaria and
Sorbaria), their ovule morphologies and position within the
locule and with respect to their obturators, is quite similar. Based
on these preliminary results we believe that combining ontogenetic,
morphological, and molecular data sets will not only contribute to
better phylogenetic resolution within the Rosaceae, but also provide a
strong basis for understanding other aspects of Rosaceae evolution.
Key words: floral morphology, floral ontogeny, phylogeny, Rosaceae