PHYLOGENY AND EVOLUTION OF CORNALES: INTEGRATING
MOLECULES, MORPHOLOGY, AND FOSSILS
Abstract
Recent advances in plant phylogenetic studies revealed that the
dogwoods and close relatives (order Cornales) represent an ancient evolutionary
lineage within the most diverse and highly specialized group of flowering plants,
the asterid group. The phylogenetic position of Cornales makes the order
critically important to the understanding of early evolution and diversification of
asterids. The order contains several morphologically diverse families with
excellent fossil records and provides an exceptional system for testing
macroevolutionary hypotheses. The major goal of the project is to reconstruct the
phylogeny of Cornales using evidence from extensive DNA sequences,
morphology, and fossils. The phylogeny will serve as the basis for definitive tests
of evolutionary hypotheses surrounding: 1) key morphological transformations
among members of the order; 2) biogeographic origin, intercontinental migration,
and radiation of major cornalean lineages; and 3) pattern and rate of molecular
evolution in relation to morphological differentiation and speciation. The
phylogeny will also provide a framework for a predictive and stable classification
within Cornales. The dogwood order has one of the most extensive fossil records
of any asterid group, allowing us to examine the evolutionary history of leaves,
flowers, fruits and pollen in this group which became widespread in the Northern
Hemisphere prior to the extinction of dinosaurs.
Plants of Cornales are common tree elements in the forests of northern
hemisphere and are widely cultivated for ornamental and medicinal uses. They
are critically important to forest ecology and many dogwood species have great
importance in horticulture. They also are medically relevant. For example,
Camptotheca acuminata is a close relative of the flowering dogwoods and it
contains a natural anti-cancer drug (camptothecin) that is considered second in
importance to taxolfor chemotherapy treatment. A robust phylogeny and
predictive and stable classification of the order will provide a basis for directing
horticultural, pharmacological, and other biological studies of these plants. In
addition, the phylogeny will help guide sustainable uses of natural resources of
the dogwoods and related plants. The extensive gene sequences to be collected
in the study will contribute significantly to the existing molecular data pool of
angiosperms and will facilitate comparative evolutionary studies at higher
taxonomic levels. Our study will be one of the first to integrate paleobotanical
data into the phylogenetic analysis of a group that also has many extant taxa
taking advantage of both morphological and molecular characters. Furthermore,
the project provides training for graduate and post-doctoral students, as well as
undergraduate students in plant evolutionary biology and systematics. Finally,
this project will add key information to the “Tree of Life” for flowering plants.