A Brief Overview of the Compositae, Lettuce and Sunflower
The Compositae (Asteraceae) is one of the largest and most diverse families of flowering
plants, comprising one-tenth of all known angiosperm species. It is characterized by the
compound inflorescence that has the appearance of a single "composite" flower from which it
derives its name. The Compositae is divided into two major subfamilies and one minor subfamily
with 12 to 18 tribes, 1,100 to 2,000 genera and 20,000 or more species (Stebbins, 1953, 1974;
Cronquist, 1981; Jansen et al., 1991). Lettuce and sunflower are representatives of each of
the two major subfamilies. The base chromosome number for the family is probably nine. All
Compositae species analyzed to date have genomes larger than 1.1 pg/1C; unfortunately none is
known to have a small genome (reviewed in Kesseli and Michelmore, 1997). The family most
likely originated 30 to 100 MYA in South America (Raven and Axelrod, 1974) and underwent
rapid and extensive diversification producing a cosmopolitan array of taxa. They are
predominantly herbaceous, although woody species also exist. Compositae are found in
diverse habitats; anaerophytic, xerophytic, and halophytic specialists thrive in some of the
more inhospitable habitats (vertisols, deserts, and salt marshes). Lactuca and Helianthus
are both drought tolerant taxa. The little known oilseed, noug (Guizotia abysinnica), is an
anaerophyte that grows on water-logged vertisols in Ethiopia and India, where few other
species and no other oilseeds can be grown. The size and adaptive success of the Compositae
have stimulated considerable research into its systematics and evolution.
The Compositae contains over 40 economically important species including food (lettuce,
Jerusalem artichoke), oil (sunflower, safflower), medicinal (chamomile) and many ornamental
(Chrysanthemum, dahlia, zinnia, marigold) crops (Table). The high quality edible oils of
sunflower, safflower, and noug are low in saturated and high in mono- and di-unsaturated
fatty acids. Additional novel industrial and edible safflower and sunflower oils have been
developed (e.g., high oleic sunflower oil). The Compositae are renowned for the production
of a variety of novel secondary chemicals. Several novel industrial fatty acids are found in
the seed oils of composites, e.g. conjugated dienolic fatty acids in Dimorphotheca,
acetylenic fatty acids in Crepis, and epoxy fatty acids in Vernonia and Stokesia (Smith,
1985). The family is a rich source of powerful insecticides and industrial chemicals, e.g.,
pyrethrum (Chrysanthemum) and rubber (guayule) (Heywood et al., 1977). Several species are
grown as medicinal and culinary herbs (Table). Echinacea and others may be sources of
biologically active compounds with medical or nutritional benefits. The Compositae also
includes several detrimental weeds (dandelion, ragweed, thistle). Lettuce and sunflower are
the best genetically characterized members of this family.
Economically Significant Members of the Compositae Family
||Genus and Species
|Lettuce||Lactuca sativa L.||Food
|Sunflower||Helianthus annuus L.||Oil, Food, and Ornamental
|Safflower||Carthamus tinctorius L.||Oil, Food, and Ornamental
|Endive||Cichorium endivia L.||Food
|Chicory||Cichorium intybus L.||Food
|Artichoke||Cynara scolymus L.||Food
|Cardoon Cynara||cardunculus L.||Food
|Jerusalem Artichoke||Helianthus tuberosus L.||Food
|Noug||Guizotia abysinnica L.||Oil and Food
|Calendula||Calendula officinalis L.||Oil, Ornamental, and Herb
|Dimorphotheca Daisy||Dimorphotheca pluvialis L.||Oil and Ornamental
|Osteospermum||Osteospermum spp.||Oil and Ornamental
|Stoke's Aster||Stokesia laevis L.||Oil and Ornamental
|Guayule||Parthenium argentatum L.||Rubber
|Pyrethrum Daisy||Chrysanthemum cinerariifolium L.||Pesticide and Ornamental
|Coneflowers||Echinacea spp.||Medicinals and Ornamentals
|Black-Eyed Susans||Rudbeckia spp.||Ornamentals
|Gerbera Daisies||Gerbera spp.||Ornamentals
|Lawn Daisy||Bellis perennis L.||Ornamental and Herb
|Tansy||Tanacetum vulgare L.||Ornamental and Herb
|Feverfew||Tanacetum parthenium L.||Ornamental and Herb
|Cotton Thistle||Onopordum acanthium L.||Ornamental and Herb
|Elecampane||Inula helenium L.||Ornamental and Herb
|Santolina||Santolina chamaecyparissus L.||Ornamental and Herb
|Curry Plant||Helichrysum angustifolium L.||Ornamental and Herb
|Sweet Joe Pye||Eupatorium purpurea L.||Ornamental and Herb
|Yarrow||Achillea millefolium L.||Ornamental and Herb
|Artemesias||Artemesia spp.||Ornamentals and Herbs
|Tarragon||Artemesia dracunculus L.||Herb
|Costmary||Chrysanthemum balsamita L.||Herb
|Chamomile||Anthemis nobilis L.||Herb
|Dandelion||Taraxacum officinale L.||Food and Weed
Lettuce (Lactuca sativa L.) is a diploid (2n = 18) species within the Lactuceae subfamily of the
Compositae (Asteraceae) and has a genome size of ~2.3 pg (Koopman & De Jong, 1996). There are four
well-established species within the subsection Lactuca, the cultivated L. sativa and three wild
species, L. serriola, L. saligna, and L. virosa (in order of decreasing sexual
compatibility with L. sativa). L. serriola is probably the progenitor of L. sativa
and may be conspecific (Kesseli et al., 1991; de Vries, 1997). Wild species, particularly
L. serriola, have been sources of several disease resistance genes (Crute, 1988); however, they
remain a rich source of variation for a range of traits that has not been accessed systematically, particularly
for horticultural traits.
Lettuce is an important crop species with an annual farm-gate value in the US of over $1.1 billion (Anon., 1995;
Davis et al., 1997). Genetic improvement programs are focused on morphology, horticultural performance,
and physiological disorders as well as disease resistance and post-harvest problems (Ryder, 1986).
Lettuce is amenable to classical and molecular genetic analyses. Most cultivars of L. sativa are highly
inbred and therefore exhibit extensive genetic homozygosity. Crosses can be made readily, although outcrossing
cannot be guaranteed. Therefore, most genetic analysis has relied on F2 rather than backcross or
test-cross populations. The generation time is usually three to five months depending on the genotype and
environment, allowing multiple generations each year. A few genotypes have generation times of less than two
months. Each plant produces large numbers (1,000s) of seeds allowing rare recombinants and mutants to be detected.
A detailed genetic map has been constructed as described (link to www address).
Cultivated sunflower (Helianthus annuus L.) is a diploid (n = 17) species belonging to subtribe Helianthinae in
the second major subfamily Asteroideae within the Compositae (Seiler and Rieseberg, 1997). The genus Helianthus
is comprised of 12 annual and 36 perennial species and belongs to the subtribe Heliantheae. Sunflower and Jerusalem
artichoke (H. tuberosus; n = 34, a perennial tetraploid) are the two significant food sources in the genus.
The centers of diversity for both species are North America (Heiser and Smith, 1955; Heiser 1976). Sunflower is one of
the few major food crops of the world that is native to temperate North America.
Sunflower is one of the most important sources of edible oil in the world. Twenty million hectares of oilseed sunflower
were produced worldwide in 1997 (USDA Statistical Reporting Service) with a yield of 24.3 million metric tons of oil and
an estimated farm-gate gross value of $37.4 billion. Confectionery and ornamental sunflowers generate additional revenues.
Cultivated sunflower is primarily grown from single-cross hybrid seed. Eighty million kg of hybrid seed were produced
and sold in 1997 with gross seed sales of $640 million. Sunflower ranked second only to maize in hybrid seed sales in 1997.
Wild Helianthus species have been important sources of genes for disease resistance, cytoplasmic male-sterility (CMS),
drought tolerance, and other traits (Jan, 1997). The development of CMS sunflower from interspecific crosses (e.g.,
H. annuus x H. petiolaris) and the fertility restorer genes from H. annuus opened the way to hybrid seed
production and the hybrid seed industry of sunflower (Leclerq, 1969; Kinman, 1970; Fick and Zimmer, 1976).
Sunflower has several characteristics that facilitate genetic analyses. Although naturally allogamous and self-incompatible,
self-compatible and strongly self-pollinated germplasm has been developed and is the core for hybrid breeding and genetic analysis.
Sunflower is a widely adapted summer annual, can be crossed without difficulty, is a prolific seed producer (1,000+
seeds/plant), and has a moderately short seed-to-seed generation time (70 to 100 days).
Domestication of both lettuce and sunflower has resulted in dramatic changes in morphology, development, and physiology. In
lettuce, the vegetative rosette has become exaggerated with a reduction in branching and a delay in flowering and bolting.
There has also been a reduction in spininess and bitter compounds. A single recessive locus determines non-shattering of the
capitulum and consequently retention of the seed. Both seed size and seedling vigor are greater in the cultivated species.
In sunflower, a single compound flower is enlarged and branching is eliminated. Seed size and seedling vigor are increased
and secondary metabolism has been modified to accentuate the accumulation of oil (Dedio 1982; Leon et al., 1996) in
the seeds. Self-incompatibility has been lost which enhances high seed yields and shattering has been eliminated to ensure
the retention of seeds for harvesting. In ancient times, lettuce was also cultivated as an oil seed crop but this is not a
Marketing lettuce from Salinas, Watsonville, other Central California districts and Colorado in 1994.
Federal State Market News Service.
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