Greek oregano
Formerly listed botanically as Origanum heracleoticum, Greek Oregano is one very
spicy herb. It's parent Origanum vulgaris, a culinary zero, is often
commercially grown and offered as Greek Oregano. O. vulgaris, often known as
Wild Marjoram, is an extremely invasive plant with a pink flower. Origanum
vulgaris hirtum is the true Greek Oregano with flavor so intense it numbs the
end of your tongue when fresh, and like all culinary oreganos, the flower of
Greek Oregano is white.

Mexican Oregano
Mexican Oregano-A Tasty Twist on an Age-Old Flavor
Plants & Gardens News Volume 20, Number 1 | Spring 2005
by Scott D. Appell
After a lifetime of growing edible plants, I've come to the conclusion that
"oregano" should be a botanical category of aroma and taste rather than the
common name for any one herb. After all, there are so many plants with the
requisite essential oils that provide oregano's heady, easily recognizable
fragrance and piquant flavor. Most folks in the U.S. are familiar with common
oregano (Origanum vulgare), and many have used Greek oregano, Italian oregano,
and Sicilian oregano-all cultivars of O. vulgare ssp. hirtum. Some even know
about Turkistan oregano (Origanum tytthantum) from central Asia and showy
oregano (O. pulchellum), which is popular in the Mediterranean region.
But the oregano experience is not confined to a single genus, Origanum. Take,
for example, Cuban oregano, or Spanish thyme, called simply orégano in Spanish.
This aromatic shrub and oregano analog is neither oregano (Origanum) nor thyme
(Thymus), nor is it from Cuba or Spain, for that matter. The scientific name of
this African native is Plectranthus amboinicus.

Mexican oregano

Origanum and Plectranthus both belong to the Lamiaceae, or mint family, so you'd
be forgiven for thinking that it's all just a family thing. But then along comes
yet another wonderful oregano wannabe: Mexican oregano (Lippia graveolens)-also
called orégano in Spanish-a member of the Verbenaceae, or verbena family. Little
known in North America, this "oregano" is a great acquisition for plant
collectors and herb gardeners alike.

Though not a true oregano, Mexican oregano is native to Mexico, as well as
Guatemala and parts of South America. A somewhat ungainly shrub, it grows up to
five feet tall and wide. Its brittle branches are very narrow, stiffly arching,
and arranged in a seemingly haphazard manner. (The plant responds extremely well
to pruning, so consider espaliers or topiaries as alternatives to the natural
zigzag form). Its dark green, highly fragrant, corrugated foliage is
minuscule-about 1/3-inch long by 1/8-inch wide. Tiny, starry-white flowers are
borne intermittently throughout the year in the leaf axils.