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bolanderi due to recent information which has shown it to be morphologically
and genetically distinct (Oliveri and Jain 1977; Rieseberg et al. 1988; Jain et
al. 1992). Third, the species name H . pauciflorus has priority over H . rigidus
and is treated accordingly herein. Fourth, Viguiera porteri has been
transferred to Helianthus porteri (Pruski 1998; Schilling et al. 1998). Fifth,
Helianthus verticillatus has recently been rediscovered and redescribed, and
is now recognized as a species (Matthews et al. 2002). Sixth, Helianthus
niveus ssp. canescens has been transferred to Helianthus petiolaris ssp. canescens
(Schilling 2006).
In the past, phylogenetic relationships of the perennial species and
polyploidy hybrids have been particularly difficult to resolve. Using the
external transcribed spacer region of the nucleus 18S-26S rDNA region,
Timme et al. (2007) revealed a highly resolved gene tree for Helianthus .
Phylogenetic analysis allowed for the determination of monophyletic annual
H. section Helianthus , a two-lineage polyphyletic H . section Ciliares, and the
monotypic H . section Agrestis , all of which were nested within the large
perennial and polyphyletic H . section Divaricati . The distribution of
perennial polyploids and known annual diploid hybrids on this phylogeny
suggested that multiple independent hybrid speciation events gave rise to
at least four polyploids and three diploid hybrids. Also provided by this
phylogeny was evidence for homoploid hybrid speciation outside of H .
section Helianthus .
Anashchenko (1979) proposed the first phylogeny for Helianthus on the
basis of different chromosome sets: the protogenome A for the perennial
forms ( Atrorubentes ) of the west coast of North America, the genome B for the
annual forms, C for the Ciliares , and the protogenome S for perennial shrubs
of South America ( Viguiera ). The Ciliares group was therefore regarded as a
separate group in Helianthus . The genome organization in Helianthus is
therefore still questionable. Chandler (1991) reviewed sunflower genomic
relationships and came to the conclusion that there is little evidence of the
existence of distinct genomes in Helianthus .
Sossey-Alaoui et al. (1998) using RAPD technology proposed a
phylogeny of 36 Helianthus species based on 33 fragments common to all the
Helianthus species. Fifty-six were unique to perennial species of sections
Atrorubentes and Ciliares , 24 were unique to section Atrorubentes , and 29
were unique to section Helianthus , whereas none were unique to section
Ciliares . Each set of common or specific fragments was assumed to belong to
a genome: (1) the C genome carrying the fragments common to all species of
the three sections, (2) the H genome unique to section Helianthus , (3) the P
genome common to perennial species sections Atrorubentes and Ciliares , (4)
the A genome unique to section Atrorubentes. The genomic structure was
therefore HC for section Helianthus , CPA for section Atrorubentes, and CP?
for section Ciliares . They also concluded that molecular hybridization with
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