From a botanical standpoint, the primary distinction lies in the scientific names. True Greek oregano is classified as Origanum vulgare subsp. hirtum (sometimes referred to as Origanum heracleoticum). It is a specific subspecies within the Origanum vulgare species. The term "common oregano" typically refers to the standard Origanum vulgare plant, which is often milder and less suited for culinary use. Many ornamental oreganos fall under this category. The key difference is that Greek oregano is a distinct, cultivated subspecies prized for its potency, while common oregano is the broader, species-level name that can encompass many less flavorful varieties.
Observing the physical structure of the plant provides the most reliable identification clues. Examine the leaves and stems closely. Greek oregano (O. vulgare subsp. hirtum) has leaves that are slightly fuzzy or hairy (pubescent) and a vibrant gray-green color. They are generally smaller and more oval-shaped. In contrast, common oregano (O. vulgare) often has smoother, brighter green, and larger leaves. The stems of the Greek variety are also typically hairier and can have a reddish tinge. Furthermore, Greek oregano grows as a low, spreading mound, whereas common oregano can often appear more upright and leggy.
The flowers are a definitive botanical identifier. Greek oregano produces abundant white flowers that are highly attractive to pollinators. The blooms are small and form in clusters at the end of the stems. Common oregano, on the other hand, frequently flowers in shades of pink or pale purple. While flower color can sometimes vary within a species, consistent white blooms are a very strong indicator that you have the Greek subspecies. It is important to note that both plants bloom in mid to late summer.
The most telling test from a culinary and aromatic perspective is to crush a leaf between your fingers and smell it. Greek oregano should release a powerfully pungent, spicy, and classic oregano aroma. Its flavor is robust and peppery. Common oregano will have a much milder, sometimes almost sweet or grassy scent with little to no pungency. Its flavor is significantly weaker. This difference in potency is due to the higher concentration of essential oils, particularly carvacrol, in Greek oregano. If your plant's scent doesn't strongly remind you of pizza or Mediterranean cuisine, it is likely the common variety.
