There are two species of wormwood that contain thujone that are used in making absinthe. They are Artemisia Absinthium and Artemesia Pontica.
Artemisia absinthium is often referred to as 'grande wormwood', which means large wormwood. It is also referred to as 'common wormwood', or simply 'wormwood'.
Artemisia pontica is often referred to as 'petite wormwood', which means small wormwood. It is also referrred to as 'roman wormwood'.
Grande wormwood (artemisia absinthium) is one of the three essential herbs required to make authentic absinthe. The other two essential herbs are green anise and fennel. These three essential herbs are often referred to as the 'Holy Trinity' of absinthe. I prefer calling them the 'Unholy Trinity' of absinthe--just to keep things in perspective!
Artemesia pontica is sometimes used in the secondary maceration (coloring step) to contribute to absinthe's green color. It is used to color absinthe due to its mild bitterness and aromatic properties. Hyssop and lemon balm are also used to color absinthe.