Basic Information - Genetics, Genomics and Breeding of Crop Plants - page 24

1.4.3 Habitat
The North American species of Helianthus are found in virtually all parts of
the United States with several species extending into Canada and a few into
Mexico. With such a diversity of species, their habitats are highly variable,
ranging from disturbed areas to tall grass prairies and to climax forests.
They occupy a variety of habitats, usually in fully open areas, but a few will
grow in rather dense shade. A number of the species could be classified as
weeds. Wild Helianthus annuus , which has the most extensive distribution of
any species, grows mostly in disturbed areas. A few of the species are endemic
to specific habitats. Helianthus exilis is restricted to the serpentine soils of the
California coastal range and Sierra Nevada Mountains in California while
H . californicus , which is indigenous to central and southern California, is
restricted to riparian habitats. Other species such as H. niveus ssp. tephrodes
are restricted to the Algodones Sand Dunes in California, and H . porteri is
endemic to granite outcrops in the Piedmont region of the southeastern
USA. Helianthus carnosus is restricted to boggy wetlands in Florida.
1.4.4 Karyotype
Karyotype analyses of sunflower are reviewed by Chandler (1991), although
the genus is of economic and evolutionary interest. Classical karyotype
describes each of the haploid chromosome sets of an organism based on
features such as length of chromosome, ratio of arm lengths, position of
centromere and secondary constrictions, and size and position of
heterochromatic knobs. Karyotype analysis has provided useful markers in
chromosome identification and the designation of chromosomes in many
plant species. Most karyotypes of Helianthus species have been conducted
with mitotic metaphase chromosome preparations in the 1970s and 1980s
(Jan and Seiler 2007). The classification of chromosomes as median (m),
sub-median (sm), sub-terminal (st), or terminal (t) when the long:short arm
ratio was in the range of 1.0 to 1.7, 1.7 to 3.0, 3.0 to 7.0, and 7.0 µ, respectively,
following the convention of Levan et al. (1964) and is used in almost all the
sunflower literature.
Karyotype studies have been conducted on H. annuus and H. debilis
(Raicu et al. 1976), H. mollis (Georgieva-Todorova et al. 1974), H. salicifolius
(Georgieva-Todorova and Lakova 1978), hybrids of H. annuus x H. hirsutus
(Georgieva-Todorova and Bohorova 1980), H. hirsutus and H. decapetalus
(Georgieva-Todorova and Bohorova 1979), cultivated H. annuus (Al-Allaf
and Godward 1977), and 12 Helianthus species (Kulshreshtha and Gupta
1981). In general, Georgieva-Todorova and Bohorova (1979, 1980) reported
large chromosome sizes, with more chromosomes classified as m and sm,
and 2 to 4 satellited chromosomes. In contrast, Kulshreshtha and Gupta