Oregano (aka Origanum vulgare/Wild Marjoram) is a different species from Marjoram (aka O. marjoram/Sweet Marjoram).
Oregano has a higher concentration of the aromatic compound carvacrol, which gives it its savory flavor. Marjoram, by contrast, contains less carvacrol and gets its aroma from the aromatic compounds sabinene (woody and fresh), terpinene (citrus), and linalool (floral).
Though similar to oregano, this blend of compounds gives Marjoram a more complex flavor profile, considered more floral, clove, pine, and sweeter than oregano’s spicy undertones. Marjoram is often preferred for cooking purposes.
Carvacrol is a phenol that is a potent inhibitor of bacterial growth and is used as a food additive to prevent food poisoning.
Both plants are in the mint family, Lamiaceae and exhibit antimicrobial, antioxidant, and anti-inflammatory properties.
Find out more about using oregano as a culinary and medicinal herb Oregano (Niu Zhi).