While both of these oregano plants look similar in the photos they have big differences. The first photo is Greek oregano, which is low growing like a groundcover. When Mexican oregano comes into bloom, the flower stems shoot up over a foot high. While various bees like lavender and germander flowers, moths are especially attracted to the Mexican oregano. I remember catching these moths when I was a kid (it is not hard to pinch the wings together when they are fully open).
In the culinary field, low-growing Greek oregano seems to me to have a stronger aroma and potency. I recently acquired a small Italian oregano plant, that has yet to flower. Have not yet done a taste comparison with the three varieties of oregano either.
I like using all of the oregano plants in the landscape, as they have some strong assets, besides their good looks. They are deer and drought resistant. The flowers are a pretty addition to a summer bouquet, but not over-powering in their scent. While the Greek oregano flowers are good for very small vases, the Mexican variety is a nice accent for mid-size flower arrangements.
susansflowers 