Lovage is a perennial. It's hard to find in England, but I've bought whole plants at garden centres, as well as at a market in Wallonia (where it's called livèche). I haven't seen it sold as a herb in shops. It tastes like very strong celery, but is more fragrant.

It should not be confused with a different herb, called ajwain, whose seeds are sometimes sold as lovage in shops which sell indian spices, where you can also buy hing, which is asafoetida, the silphium substitute.