Reference point
Crushed leaves of purple holy basil.
Do this before you read on. An entry only works when you have just smelled the thing.
Green laid straight on top of a clove base so clear it cannot be mistaken. The two layers do not blend but sit one on the other, and you can separate them by smelling slowly.
This entry bridges the green family and the spicy family. It is also living proof of the chemotype concept. Within the same genus, Ocimum, there are varieties of quite different chemical nature: one rich in eugenol that smells of clove, another rich in methyl chavicol that smells of anise.
If you have ever wondered why Italian basil and Thai basil do not smell alike despite sharing a botanical name, the answer is here.
How to smell it
Crush a leaf of purple holy basil and smell it at once. Then smell a dried clove bud. You will recognise what they share immediately. If you have Thai basil, smell that too to see how far one genus can travel.
Why this one is hard
People often treat the botanical name as a guarantee of smell. It is not. A species name speaks of form and genetics; smell depends on the compounds the plant makes, and that varies with soil, altitude and season.
Don’t confuse with
This entry
Holy basil
Green family
Both contain eugenol, so both have a clove note. But holy basil is a fresh leaf, with a green layer on top; clove is a dried bud, dense, and numbs the tongue.
Scientific note
Holy basil is the clearest example of a chemotype in Vietnam. It belongs to the same genus as basil, Ocimum, but depending on the variety the plant accumulates eugenol or methyl chavicol as its dominant compound.
One point needs to be clear: this is a genetic difference between varieties, not a plant switching direction when it is moved. The environment adjusts the amounts; it does not change the dominant compound. Take seed from a eugenol-rich variety and grow it elsewhere, and you still get a eugenol-rich plant.
In Vietnamese life
Holy basil is the main ingredient of the traditional herbal steam bath for colds, usually together with lemongrass, pomelo leaf and mint. Together the four make a smell that almost everyone in Vietnam recognises instantly but few can take apart.