They're mostly discussed in the supplements & herbs section, that's why you don't see them very often here.
My experience with herbs was that most are very weak. Rhodiola is alright, so are a few others. But let's take scullcap as an example: its mechanism (I think) is GABA receptor modulation, the same as prescription anxiety meds (benzos) but a lot weaker. So it likely comes with exactly the same problems and risks, scaled down to its level of activity. If you made a concentrated exctract of a herb like scullcap, you could probably demonstrate tolerance & dependence, and a benzo or alcohol like effect. Herbs contain drugs if they are active in any way. Some of the most famous drugs could be called herbs, like cannabis, opium, coca. The active chemicals just happen to be a lot more potent.
Back to the point... rhodiola is my favourite herb. It has a noticeable mood lift and, if you don't dose too high, anxiety relieving action. Feels like a mild stimulant. One of the mechanisms shown was COMT inhibition, which is used in a type of Parkinson's medication to raise dopamine. It also feels like it has a mild opioid like effect, no idea what the mechanism is.
Also, sceletium tortuosum AKA kanna. Some places claim it's an SSRI, but I've only seen evidence for it being a PDE-4 inhibitor (which is a far more interesting action). I tried smoking it and got a very light mood lift, but didn't do it properly or smoke much... In fact I think I'll buy some and stick it in my Volcano!