What herb is this?

Factual Questions
21

The first thing I thought of when I saw it was that it reminds me of mint, or maybe lemon balm. This article lists many of the mint family, maybe your friend’s plant is on there?

22

I would say it looks a hell of a lot like Thai basil (I used to grow some), but I wouldn’t be able to tell 100% without rubbing it on my fingers and smelling it.

23

No, lemon balm doesn’t have leaves like that. They’re bumpy, like this.

24

The three-lobed leaf (note the two small lobes on each side of the petiole) excludes any mint or basil.

25

See also here:
http://images.google.ch/images?client=firefox-a&rls=org.mozilla:fr:official&channel=s&hl=fr&q=salvia%20verticillata&lr=lang_en&oe=UTF-8&um=1&ie=UTF-8&sa=N&tab=wi

or search Google “Salvia verticillata”, then “images”

26

Nice catch. I didn’t even see that.

27

Every time I see the thread title the first few bars of “Greensleeves”/“What Child Is This?” goes though my head. "What herb is this dum dum dum dum… "

28

Gymnopithys, the leaves on the OP’s photo don’t look at all like the leaves on salvia verticillata to me.

For comparison, here are two photos from your linked page. The salvia’s leaves are more shield-shaped, with a ruffled edge.