MCNEAL, JOEL R.* AND CLAUDE W. DEPAMPHILIS. Department of Biology and Institute of Molecular Evolutionary Genetics, Penn State University, University Park, PA 16802. - Origin and molecular systematics of the parasitic plant genus Cuscuta (dodder).
The genus Cuscuta is composed of a large number of
morphologically similar stem parasitic vines. They produce minute,
scale-like leaves with flower structure that is often only discernable
microscopically. The morphological reduction of Cuscuta has
historically rendered them a taxonomically difficult group, although
most authorities have agreed they are allied to Convolvulaceae
(Morning Glories). Even molecular systematic approaches have proven
confounding, as the chloroplast and nuclear genes most often used in
broad phylogenies have been shown to evolve at accelerated rates in
parasitic plants, sometimes leading to incorrect phylogenetic
inferences. Mitochondrial gene and intron sequences have revealed a
sister relationship of Cuscuta to members of Convolvulaceae
rather than suggesting Cuscuta is nested within the family. A
Nuclear ITS phylogeny provides insights into the relationships between
the three traditionally recognized subgenera of Cuscuta along
with a more detailed interspecific phylogeny. These relationships
have a significant impact on the understanding of the evolution of
parasitism and photosynthesis in Cuscuta.
Key words: Convolvulaceae, Cuscuta, ITS, mitochondrial DNA, parasitic plant, systematics