French marigold

Author: Hon A/Prof Marius Rademaker, Dermatologist, Hamilton, New Zealand, 2004.

Common name: French marigold, African marigold, Mexican marigold, Indian marigold, Stinking Roger, Khaki weed. Pot marigold belongs to a different genus (Calendula).
Botanical name: Tagetes spp.: Tagetes erecta, Tagetes lucida, Tagetes minuta, Tagetes patula.
Family: Compositae/Asteraceae (daisy/aster family)
Origin: Despite its common name, the African marigold (T. erecta) and French marigold (T. patula) are native to Mexico and Central America. These plants were brought from the new world to Europe in the 16th century. Marigolds have naturalized to many warm climate areas all over the world.
Description: Marigolds are categorized into three groups: French, African and triploid marigolds. The French marigolds (Tagetes patula) are small bushy plants that are 15-30 cm in height. The flowers are up to 5 cm across and are composed of a dense arrangement of ‘rays’ that come in yellow, orange and a unique bronze colour. The French marigolds bloom continuously until cut down by frost. The African marigolds (Tagetes erecta), also called American marigolds, are tall stout plants that grow to 1 m in height. They have larger blossoms and a shorter flowering period than their French cousins. The triploid marigolds are sterile hybrids obtained by crossing the French with the African species. These triploids are non-stop bloomers with impressive 7-8 cm flower heads in clear warm colours of gold, yellow, red and russet. The leaves of all marigolds are dark green, deeply divided and have a somewhat unpleasant, aromatic fragrance.
Uses: Marigold flower petals are fed to chickens, which imparts a yellow hue to the meat and fat. Another Tagetes species is commonly called Mexican tarragon (Tagetes lucida). It is used in the kitchen as a substitute for the more familiar French tarragon. Other species are used in perfumery.
Allergens: Sesquiterpene lactones are thought to be the main sensitizers of the Compositae family. Other possibly allergens are the thiophenes which include 5-(3-buten-1-ynyl)-2,2'-bithiophene, alpha-terthienyl and hydroxytremetone.
Allergy: Several species of Tagetes are strongly aromatic and potentially irritant. As early as 1895, allergy to Tagetes minuta was reported. Tagetes indica is well known to cause an airborne contact dermatitis in India. The prevalence varies from 0.7-1.4% in the general population, up to 4.5% among occupationally exposed persons. Compositae allergy is among the top ten contact sensitivities in Europe. Tagetes minuta has become a major weed in parts of Africa; the sap causes chemical irritation and possible allergy. There are reports of occupational dermatitis to Tagetes patula in an aromatherapist.
Cross reactions: Arnica montana.
Other information:  
Patch test: Leaf, as is, sesquiterpene, compositae mix.

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