Bergamot

A citrus, but a complicated one. Bergamot has the brightness of lemon with a floral softness over the top and a faint bitterness underneath — more interesting than any other citrus and harder to place.

Most people have smelled it without knowing: bergamot is what makes Earl Grey taste like Earl Grey. If a blend smells vaguely of good tea, this is usually the reason.

It is a top note, so it leads, but it is less fleeting than lemon and tends to bridge into the heart of a blend rather than disappearing off a cliff. That makes it one of the more useful openers in a diffused fragrance, where you want the first impression to connect to what follows.