Common or wild oregano is a perennial plant native to the Mediterranean region and Asia and cultivated in the United States. Its creeping rootstock produces a square, downy, purplish stem with opposite ovate leaves. Stems can grow up to 76 cm tall and are dotted with small depressions.
https://www.drugs.com/npp/oregano.html
There is no clinical evidence to support specific therapeutic doses of oregano; however, due to its wide use in foods, it has been designated GRAS (generally recognized as safe) status by the FDA. In a small study, 200 mg/day emulsified O. vulgare oil was administered for 6 weeks.
https://www.drugs.com/npp/oregano.html
To obtain oregano oil, the dried flowers and leaves of the wild oregano plant are harvested when the oil content of the plant is at its highest, and then distilled. The resulting oil is golden to dark yellow, with a strong spicy odor.
http://articles.mercola.com/herbal-oils/oregano-oil.aspx
1 Several Turkish species of Origanum are also found in commerce, including O. onites L. and O. syriacum L. 4 Other taxa in the genera Coridothymus , Thymbra , and Satureja have similar chemistry. 4 Lippia graveolens Kunth. (Verbenaceae) is known as Mexican oregano.
https://www.drugs.com/npp/oregano.html
Allergic contact dermatitis caused by spices, including oregano, is well documented. 88 Although oregano is frequently consumed, there are a few reports of adverse or systemic reactions. One report of anaphylaxis exists, and cross-sensitivity with other members of the Lamiaceae family has been noted.
https://www.drugs.com/npp/oregano.html
Story at-a-glance -. Oregano oil is derived from the leaves and flowers of oregano (Origanum vulgare), a hardy, bushy perennial herb, and a member of the mint (Lamiaceae) family. The most therapeutically beneficial is the oil produced from wild oregano or Origanum vulgare that's native to Mediterranean regions.
http://articles.mercola.com/herbal-oils/oregano-oil.aspx
1 Water thoroughly, only when the soil is dry to the touch.  Spacing: Plant oregano eight to 10 inches apart in your garden. Oregano grows up to two feet tall and spans about 18 inches across. If you are planting oregano in a container, be sure the pot is about 12 inches in diameter; oregano is a prolific grower.
http://www.thekitchn.com/everything-you-need-to-know-about-growing-oregano-220612
1 The most therapeutically beneficial is the oil produced from wild oregano or Origanum vulgare that's native to Mediterranean regions.  The most therapeutically beneficial is the oil produced from wild oregano or Origanum vulgare that's native to Mediterranean regions.
http://articles.mercola.com/herbal-oils/oregano-oil.aspx
I think the Greeks got it right when they described oregano as joy of the mountain.. This aromatic, ancient culinary herb, also referred to as wild marjoram, originates from the hilly, Greek countryside, and is now grown all over the world. Oregano is a must-have in a culinary garden. Its pungent, spicy, slightly bitter flavor pairs well with almost any vegetable preparation.
http://www.thekitchn.com/everything-you-need-to-know-about-growing-oregano-220612
Oregano oil is derived from the leaves and flowers of oregano (Origanum vulgare), a hardy, bushy perennial herb, and a member of the mint (Lamiaceae) family. It's native to Europe, although it grows in many areas around the world.
http://articles.mercola.com/herbal-oils/oregano-oil.aspx
what is  oregano
Oregano is a perennial plant native to the Mediterranean region and Asia and cultivated in the United States.