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Calendula officinalis (pot marigold) is a plant in the genus Calendula (pot marigolds), in the family Asteraceae. It is probably native to southern Europe though its long history of cultivation makes its precise origin unknown, and may possibly be of garden origin. It is also widely naturalised further north in Europe (north to southern England) and elsewhere in warm temperate regions of the world.<ref name=flora>Interactive Flora of NW Europe: Calendula officinalis</ref><ref name=pfaf>"Calendula officinalis - L." (HTML). Plants For A Future. June 2004. http://www.pfaf.org/database/plants.php?Calendula+officinalis. Retrieved 2007-12-19. </ref><ref name=rhs>The New RHS Dictionary of Gardening 1: 462.</ref>
It is a short-lived aromatic perennial plant, growing to 80 cm tall, with sparsely branched lax or erect stems. The leaves are oblong-lanceolate, 5–17 cm long, hairy on both sides, and with margins entire or occasionally waved or weakly toothed. The inflorescences are yellow, comprising a thick capitulum or flowerhead 4–7 cm diameter surrounded by two rows of hairy bracts; in the wild plant they have a single ring of ray florets surrounding the central disc florets. The disc florets are tubular and hermaphrodite, and generally of a more intense orange-yellow colour than the female, tridentate, peripheral ray florets. The flowers may appear all year long where conditions are suitable. The fruit is a thorny curved achene.<ref name=flora/><ref name=rhs/>
Synonyms include Calendula officinalis var. prolifera. Other recorded English names include Ruddles, Common Marigold, Garden Marigold, English Marigold, and Scottish Marigold.<ref name=rhs/>
Calendula officinalis is widely cultivated as a herb and can be grown easily in sunny locations in most kinds of soils. Although perennial, it is commonly treated as an annual plant, particularly in colder regions where its winter survival is poor, or in hot summer locations where is also does not survive.
Calendula are considered by many gardening experts as one of the most versatile flowers to grow in a garden, especially since they are easy to grow, and tolerate most soils. In temperate climates, sow seed in spring for blooms that last throughout the summer and well into the fall. In areas of little winter freezing (USDA zones 8-11), sow seeds in autumn for winter color, plants will wither in subtropical summer. Seeds will germinate freely in sunny or half-sunny locations, but plants do best if planted in sunny locations with rich, well-drained soil. Pot marigolds typically bloom quickly from seed (in under two months) in bright yellows, golds, and oranges.
Leaves are spirally arranged, 5–18 cm long, simple, and slightly hairy. The flower heads range from pastel yellow to deep orange, and are 3–7 cm across, with both ray florets and disc florets. Most cultivars have a spicy aroma. It is recommended to deadhead (removal of dying flower heads) the plants regularly to maintain even blossom production.
Numerous cultivars have been selected for variation in the flowers, from pale yellow to orange-red, and with 'double' flowerheads with ray florets replacing some or all of the disc florets. Examples include 'Alpha' (deep orange), 'Jane Harmony', 'Sun Glow' (bright yellow), 'Lemon' (pale yellow), 'Orange Prince' (orange), 'Indian Prince' (dark orange-red), 'Pink Surprise' (double, with inner florets darker than outer florets) and 'Chrysantha' (yellow, double). 'Variegata' is a cultivar with yellow variegated leaves.<ref name=rhs/>
Calendula are used as food plants by the larvae of some Lepidoptera species including Cabbage Moth, The Gothic, Large Yellow Underwing and Setaceous Hebrew Character. Be advised not to plant in vegetable gardens.
Pot marigold florets are considered edible. They are often used to add color to salads, or added to dishes as a garnish and in lieu of saffron. The leaves are edible but are often not palatable. They have a history of use as a potherb and in salads.
Calendula officinalis is used for the treatment of skin disorders and pain, and as a bactericide, antiseptic and anti-inflammatory. The petals and pollen contain triterpenoid esters (an anti-inflammatory) and the carotenoids flavoxanthin and auroxanthin (antioxidants, and the source of the yellow-orange coloration). The leaves and stems contain other carotenoids, mostly lutein (80%) and zeaxanthin (5%), and beta-carotene. Plant extracts are also widely used by cosmetics, presumably due to presence of compounds such as saponins, resins and essential oils.<ref>National Institutes of Health. "Calendula" (HTML). Herbs and Supplements. U.S. National Library of Medicine. http://www.nlm.nih.gov/medlineplus/druginfo/natural/patient-calendula.html. Retrieved 2007-12-19. </ref>
The flowers of Calendula officinalis contain flavonol glycosides, triterpene oligoglycosides, oleanane-type triterpene glycosides, saponins, and a sesquiterpene glucoside.<ref>Ukiya M, Akihisa T, Yasukawa K et al. Anti-inflammatory, anti-tumor-promoting, and cytotoxic activities of constituents of pot marigold (Calendula officinalis) flowers. (2006). J Nat Prod. 69:1692-1696.</ref><ref>Yoshikawa M, Murakami T, Kishi A et al. (2001). Medicinal flowers.III. Marigold.(1): hypoglycemic, gastric emptying inhibitory, and gastroprotective principles and new oleanane-type triterpene oligolycosides, calendasaponins A, B, C, and D, from Egyptian Calendula officinalis. Chem Pharm Bull. 49:863-70.</ref>
Plant pharmacological studies have suggested that Calendula extracts have anti-viral, anti-genotoxic and anti-inflammatory properties.<ref name="Jimenez-Medina E 2006">Jimenez-Medina E, Garcia-Lora A, Paco L et al. (2006). A new extract of the plant Calendula officinalis produces a dual in vitro effect: cytotoxic anti-tumor activity and lymphocyte activation. BMC Cancer. 6:6.</ref> Calendula in suspension or in tincture is used topically to treat acne, reducing inflammation, controlling bleeding and soothing irritated tissue.