There are several different flowers known as "marigolds" that belong to distinct genera: Bidens tripartita, Caltha palustris, and Calendula officinalis, and the genus Tagetes. These are the hardy annual flowers in hues of yellow, gold, orange and mahogany, sometimes red or white. These marigolds are indigenous to the American Southwest to Mexico, and to South America, but they were spread throughout the world by early colonists.
One of the quintissential experiences of my life was the 70-mile drive between Santa Barbara, California and Vandenberg Air Force Base where I worked in the 1960s. Driving north over Santa Ynez mountains, there is a panoramic view of Burpee's flower fields, known as Floradale Farms at Lompoc [pronounced "lom poke"], California. Huge fields of red, orange, lavender, pink, and yellow were the test gardens of the W. Atlee Burpee company. The Burpee company favored the marigold in developing new hybrids. In 1954 the company sponsored a contest for the production of the first white marigold. The $10,000 prize went to Alice Volk of Iowa for the first all white marigold, 'Snowbird'
Today, white marigolds are widely available . In this season's catalog, the Burpee Company offers 23 cultivars, including four all white marigolds .
In 1960 David Burpee championed marigold as the national flower and registered himself as a lobbyist in Washington D.C. to promote marigolds. Burpee convinced Illinois Senator Everett Dirksen, who at first favored the corn tassle, to support the marigold. Senator Dirksen's speech to nominate the marigold as the national flower became one of the classic speeches of American history . Propoponents supporting the rose as the national flower won out.
An annual five-day Marigold Festival is held annually at Pekin, Illinois in honor of Senator Dirksen . Festivals featuring marigold date at least to the time of Aztecs in Mexico. As marigolds were introduced around the world they were incorporated in National festivals as far away as India. Marigolds were introduced to India by early Portuguese colonists and today are produced in commerically for use in traditional Indian festivals.
As marigolds were introduced around the world by Portuguese and Spanish colonists in the 16th century, they were embraced and accepted into the deepest part of every culture. In India marigolds became the symbolic flower used in religious ceremonies, weddings, and festivals. Temples are draped with marigolds strung into garlands  and the demand is so great, marigold production has become a major commercial enterprise in that country . The main types produced for Indian markets are Tagetes erecta (African marigold), Tagetes patula (French marigold) and Tagetes tenuifolia (striped marigold) .
There are some 50 species of marigolds within the genus Tagetes. The most common marigolds found in markets are Tagetes patula, French Marigolds and Tagetes erecta or hybrids between these two species .
The modern African marigold, Tagetes erecta, grows to around 36 inches tall usually with double ball-shaped flowers. They have a distinctively unpleasant scent.
Wild Tagetes erecta, like this one offered by Seeds of Change, may have single orange flowers and grow into a large shrub.
Tagetes erecta, Cempoalxochitl marigold is a wild marigold from Oaxaca, Mexico. This is the marigold used to honor the Aztecs in the Day of the Dead festival, El Dia de los Muertos, November 1st . It grows into a shrub 5 feet tall and 4 feet wide. According to the catalog description, it has a "richly intense aroma".
The distinctive scent of marigolds is due to the substance turpene, which they contain. But not all marigolds have a distasteful scent. In fact some marigolds produce oils that are used in the manufacture of perfume.
6. Tagetes erecta 'Sweet Cream'
3. Tagetes erecta 'Simba'
4. Tagetes erecta 'Inca II Primrose'
5. Tagetes erecta 'Eskimo'
2. Tagetes erecta. Antigua Mix
7. Tagetes erecta 'French Vanilla'
French Marigolds are colorful, low-growing plants that are sometimes grown among vegetables because they deter rootknot nematode . The best method for preventing nematodes is to grow the marigolds and turn them under, then plant the nematode susceptible plants the following season. French marigolds grow to 6 to 8 inches high and have 2 inch flowers. Burpee's 'Nema-gone' French marigold  was designed for this purpose. French marigolds, like most marigolds, are especially attractive to butterflies. The hybrids, though, do not produce enough pollen to attract butterflies .
8. Tagetes petula 'Little Hero Fire'
9. Tagetes petula 'Disco Red'
10. Tagetes petula 'Moonlight'
11. Tagetes petula 'Janie flame'
12. Tagetes petula 'Harlequin'
13. Tagetes petula 'Durango Red'
Signet marigolds, Tagetes tenuifolia (or Tagetes signata) are small delicate plants to around 8 inches tall with lemon-scented foliage and a citrus flavor. The flowers which may be yellow, orange, rust, or red, are edible and the plant have a spicy tarragon flavor. Examples are 'Golden Gem' and 'Lemon Gem'. The flowers are edible and may be served in herbal salads . Like most marigolds, signet marigolds are attractive to butterflies.
14. Tagetes tenuifolia 'Lemon Gem'
15. Tagetes tenuifolia 'Paprika Gem'
16. Tagetes tenuifolia 'Golden Gem'
Tagetes filifolia (aka Irish lace) has lacy leaves and tiny white flowers, as seen in this photo. Tagetes lemmonii, (Mount Lemmon marigold) is native to southern Arizona and is also called the tangerine-scented marigold as the leaves of the plant have a strong scent of mint and lemon. The plant grows to about 3 feet. (photograph at left)
17. Tagetes lemmonii 'Mountain Marigold'
Tagetes lucida, (Spanish tarragon) has the scent of licorice or anise and can be used as a substitute for French Tarragon in cooking . (photograph left).
Tagetes lucida 'Anisata', (Sweet marigold) is a low growing marigold, growing 12 inches height with a spread of 18 inches . It has tiny golden flowers on lime green foliage. This marigold is also called sweet mace .
Tagetes minuta, is used in site preparation to deter nematodes and also for its antiviral properties for plant diseases . There is a patent of the antiviral properties of the oil extracted from Tagetes minuta. Oil extracted from Tagetes minuta is both a fragrance (citrus), an anti-inflamatory used to treat wounds and skin infections, and an insect repellent .
Marigolds are very easy to grow. Just direct sow in average soil in a sunny place after all danger of frost. Deadhead spent blooms to keep them coming.
18. Tagetes lucida 'Spanish Tarragon'
Several years ago the Burpee company tested and marketed a series of odor-less marigolds. Marigold lovers rejected the idea. People who love marigolds think they should smell like marigolds.
Kell. September 26, 2003. Tagetes petula. 'Harlequin'. Plant Files.
Per Annes Annuals where I bought this plant: "this antique Marigold from 1870 is enjoying a revival in England where it is very popular as a cut flower. Each eye catching mahogany-red petal is distinctively divided by a yellow stripe. The bush 24-36 inch tall uniform plant produces lots of blooms" And its true! A fun plant.
I am a retired archeologist and curator of an historic house museum. I live in Greensboro, Alabama, a small rural historic Southern town, with my two dogs, a rabbit and (by recent count) two cats. I am upgrading a 100 year old neoclassic house and clearing and planting my two-and-one-half acre property. Of plants, I love roses best of all.