|field marigold (Calendula arvensis)|
Calendula (//), pot marigold (US) or marigold (UK), is a genus of about 15–20 species of annual and perennial herbaceous plants in the daisy family Asteraceae. They are native to southwestern Asia, western Europe, Macaronesia, and the Mediterranean. Other plants are also known as marigolds, such as corn marigold, desert marigold, marsh marigold, and plants of the genus Tagetes. The name calendula is a modern Latin diminutive of calendae, meaning "little calendar", "little clock" or possibly "little weather-glass". The common name "marigold"  refers to the Virgin Mary. The most commonly cultivated and used member of the genus is the pot marigold (Calendula officinalis). Popular herbal and cosmetic products named 'calendula' invariably derive from C. officinalis.
Traditional and ancient uses
Calendula species have been used traditionally as culinary and medicinal herbs. The petals are edible and can be used fresh in salads or dried and used to color cheese or as a replacement for saffron. A yellow dye has been extracted from the flowers.
Romans and Greeks used the golden calendula in many rituals and ceremonies, sometimes wearing crowns or garlands made from the flowers. One of its nicknames is "Mary's Gold," referring to the flowers' use in early Catholic events in some countries. Calendula flowers are sacred flowers in India and have been used to decorate the statues of Hindu deities since early times.
Plant pharmacological studies have suggested that Calendula extracts have antiviral, antigenotoxic, and anti-inflammatory properties in vitro. In herbalism, Calendula in suspension or in tincture is used topically for treating acne, reducing inflammation, controlling bleeding, and soothing irritated tissue. Limited evidence indicates Calendula cream or ointment is effective in treating radiation dermatitis. Topical application of C. officinalis ointment has helped to prevent dermatitis, pain, and missed radiation treatments in randomized trials.
Calendula has been used traditionally for abdominal cramps and constipation. In experiments with rabbit jejunum, the aqueous-ethanol extract of C. officinalis flowers was shown to have both spasmolytic and spasmogenic effects, thus providing a scientific rationale for this traditional use. An aqueous extract of C. officinalis obtained by a novel extraction method has demonstrated antitumor (cytotoxic) activity and immunomodulatory properties (lymphocyte activation) in vitro, as well as antitumor activity in mice.
Calendula species have been used in cooking for centuries. The flowers were a common ingredient in German soups and stews, which explains the nickname "pot marigold". The lovely golden petals were also used to add color to butter and cheese. The flowers are traditional ingredients in Mediterranean and Middle Eastern dishes. Calendula tea provides health benefits, as well as being delicious.
The beautiful flowers were once used as a source of dye for fabrics. By using different mordants, a variety of yellows, oranges and browns could be obtained.
Ancient people speculated that calendula had medicinal properties. In some of the earliest medical writings, calendula was recommended for treating ailments of the digestive tract. It was used to allegedly detoxify the liver and gall bladder. The flowers were applied to cuts and wounds, presumably to stop bleeding, prevent infection and speed healing. Calendula was also used for various women's ailments, and to treat a number of skin conditions. During the American Civil War, calendula flowers were used on the battlefields in open wounds as an alleged antihemorrhagic and antiseptic agent, and they were used in dressing wounds to promote healing. Calendula also was used in this way during World War I. Calendula has been historically significant in medicine in many cultures, and it is still important in pseudomedicine today. 
- Calendula arvensis (Vaill.) L. – field marigold, wild marigold
- Calendula denticulata Schousb. ex Willd.
- Calendula eckerleinii Ohle
- Calendula incana Willd.
- Calendula incana subsp. algarbiensis (Boiss.) Ohle
- Calendula incana subsp. maderensis (DC.) Ohle – Madeiran marigold
- Calendula incana subsp. maritima (Guss.) Ohle – sea marigold
- Calendula incana subsp. microphylla (Lange) Ohle
- Calendula lanzae Maire
- Calendula maritima Guss. - sea marigold
- Calendula maroccana (Ball) Ball
- Calendula maroccana subsp. maroccana
- Calendula maroccana subsp. murbeckii (Lanza) Ohle
- Calendula meuselii Ohle
- Calendula officinalis L. – pot marigold, garden marigold, ruddles, Scottish marigold
- Calendula palaestina Boiss.
- Calendula stellata Cav.
- Calendula suffruticosa Vahl
- Calendula suffruticosa subsp. balansae (Boiss. & Reut.) Ohle
- Calendula suffruticosa subsp. boissieri Lanza
- Calendula suffruticosa subsp. fulgida (Raf.) Guadagno
- Calendula suffruticosa subsp. lusitanica (Boiss.) Ohle
- Calendula suffruticosa subsp. maritima (Guss.) Meikle
- Calendula suffruticosa subsp. monardii (Boiss. & Reut.) Ohle
- Calendula suffruticosa subsp. tomentosa Murb.
- Calendula tripterocarpa Rupr.
- Sunset Western Garden Book, 1995:606–607
- Calendula. Flora of China.
- Shorter Oxford English Dictionary, 6th ed. United Kingdom: Oxford University Press. 2007. p. 3804. ISBN 0199206872.
- Spotlight on Marigold. The Complete Herbal - Herbs and Herbal Remedies.
- Ukiya, M., et al. (2006). Anti-inflammatory, anti-tumor-promoting, and cytotoxic activities of constituents of pot marigold (Calendula officinalis) flowers. J Nat Prod. 69 1692-96.
- Yoshikawa, M., 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.
- Okoh, O. O., et al. (2008). The effects of drying on the chemical components of essential oils of Calendula officinalis L. African Journal of Biotechnology 7(10) 1500-02.
- Jimenez-Medina, E., 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.
- Duran, V; Matic, M; Jovanovć, M; Mimica, N; Gajinov, Z; Poljacki, M; Boza, P (2005). "Results of the clinical examination of an ointment with marigold (Calendula officinalis) extract in the treatment of venous leg ulcers". Int J Tissue React. 27 (3): 101–6. PMID 16372475.
- Pommier, P., et al. (2004). Phase III randomized trial of Calendula officinalis compared with trolamine for the prevention of acute dermatitis during irradiation for breast cancer. J Clin Oncol. 22(8) 1447-53.
- McQuestion, M. (2006). Evidence-based skin care management in radiation therapy. Semin Oncol Nurs". 22 163-73.
- Bolderston, A., et al. (2006). The prevention and management of acute skin reactions related to radiation therapy: a systematic review and practice guideline. Support Care Cancer. 14 802-17
- Bashir S, Janbaz KH, Jabeen Q et al. (2006). Studies on spasmogenic and spasmolytic activities of Calendula officinalis flowers. Phytother Res. 20:906-910.
- "About Herbs, Botanicals & Other Products: Calendula". Memorial Sloan-Kettering Cancer Center.
- Reider, N; Komericki, P; Hausen, BM; Fritsch, P; Aberer, W (2001). "The seamy side of natural medicines: Contact sensitization to arnica (Arnica montana L.) and marigold (Calendula officinalis L.)". Contact dermatitis 45 (5): 269–72. doi:10.1034/j.1600-0536.2001.450503.x. PMID 11722485.
- Flann, C., ed. "Species of Calendula". Global Compositae Checklist. Retrieved 31 March 2011.