KADEREIT, JOACHIM W. AND AARON LISTON.* Institut für Spezielle Botanik und Botanischer Garten, Johannes Gutenberg-Universität D-55099 Mainz, Germany and Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331. - The phylogenetic and biogeographical affinities of four annual species of Senecio native to western North America.
The phylogenetic and biogeographic affinities of four annual
Senecio species, considered native to western North America,
are examined. Senecio mohavensis, a species of the Sonoran and
Mohave deserts, is a recent derivative of the East Mediterranean S.
flavus subsp. breviflorus (sect. Senecio). Data
from nuclear ribosomal DNA internal transcribed spacer (ITS) sequences
support previous chloroplast DNA and isozyme conclusions for the
origin of S. mohavensis by long distance dispersal. Senecio
flavus subsp. flavus appears to be of South African
ancestry, while S. flavus subsp. breviflorus has
evidently hybridized with S. vernalis or S. glaucus,
acquiring the cpDNA and ITS of these Mediterranean species. Two
Californian species, S. aphanactis and S. californicus,
based on morphological evidence, may also belong to sect.
Senecio. Senecio ertterae, known from a single canyon
in eastern Oregon, is apparently derived from North American species.
These hypotheses will be examined with ITS sequence data. Considering
the imminent disassembly of Senecio sensu lato, it is important
to determine which species belong to the clade that contains the
nomenclatural type of the genus, S. vulgaris. These species
may remain the only North American members of Senecio sensu
stricto.
Key words: Asteraceae, biogeography, ITS, long distance dispersal, phylogeny, Senecio sect. Senecio