SAAR, DAYLE E.*, NEIL O. POLANS, MELVIN R. DUVALL, and PAUL D. SøRENSEN. Dept. of Biological Sciences, Northern Illinois University, DeKalb, IL 60115-2861. - A phylogenetic analysis of Dahlia (Asteraceae).
The genus Dahlia Cav. presently consists of 30 species,
primarily from Mexico. Species are usually placed in four subgeneric
sections: Pseudodendron, Epiphytum, Entemophyllon, and
Dahlia, based largely on morphological characters, supplemented
with cytological, geographical, and biochemical data. Combined
molecular sequence data from both the internal and external
transcribed spacer regions (ITS and ETS), located within the nuclear
ribosomal gene repeat unit, were used to infer a phylogeny of the
genus. Basal nodes were also supported by RAPD data. Sect.
Entemophyllum appears to be very distinct from the remainder of
the genus in almost every parameter measured. Dahlia merckii
and D. tubulata are also quite distinct, both from each other
and the remaining taxa. Sections Pseudodendron and
Epiphytum are closely allied with each other as well as with a
few species from sect. Dahlia, and this clade, the variable
root clade (VRC), incorporates all species with unusual root forms,
along with some species exhibiting the more typical tuberous type. The
remaining species of sect. Dahlia form a well-defined clade,
the core Dahlia clade (CDC). Comparisons of this phylogeny with
morphological characters suggest some traits of an ancestral
Dahlia.
Key words: Coreopsideae, Dahlia, ETS, external transcribed spacer, Heliantheae s.l., internal transcribed spacer