Lavender

Here in the south of France there's loads of lavender, and it's got many uses. The name probably comes from the Latin "to wash" (lavare) but might have its origins elsewhere...

If it's not grown decoratively, it is usually used for production of essential oils - lavender essential oil has found its way into much modern quackery:
- calming rub
- stops runny noses
- burns
- cuts and bruises
- ear pain
- monthly cramps
- anti-stress
All of the above can be magically treated by lavender. The oils do have some antiseptic and anti-inflammatory properties, but it's perhaps safest to use lavender in cooking - it's often included in "herbes de Provence". Bees use the flowers to make some very nice honey too, and if you get up close to lavender in the summer you'll find it alive with insects:

And there's money to be made in selling it - a large bunch will cost nearly $500, or in the old days you could get 50 free haircuts. Flower power.