Now that the Green Swizzle has arisen in the Falernum discussion, perhaps it’s time to dig in a little to wormwood bitters?
The Green Swizzle is an island drink that was around in the first couple decades of the 20th Century before fading out (and being replaced by a different Green Swizzle that involves green crème de menthe). @Splificator and @dsoneil write about the Green Swizzle in the in the OCS (p. 335-6) and it also gets an earlier section in the revised edition of Imbibe! In this case the wormwood bitters is “a simple infusion of wormwood and strong rum”.
Sounds like a Caribbean island version of a simple Old World remedy: snip some sprigs of whatever species of artemesia you’ve got in your back yard, cover them in whatever alcohol you’ve got, strain when ready. The art, I presume, is in selecting the infusion components and recognizing when to arrest it.
Back in 2011, @dsoneil published a more elaborate whiskey-based recipe from the Standard Manual of Soda. I presume the wormwood in that recipe is dried.
Wormwood bitters were commercialized back in the 19th Century, and this old post by Ferdinand Meyer shows off some intriguing advertising. There are a pile of commercial “wormwood bitters” on the market, today. Most seem to be from dubious cottage industries. I have a bottle of the one Berkshire Mountain Distillers made for Cocktail Kingdom, and it’s in a dasher bottle, tastes straight bitter and is obviously spiced with cloves (and probably something else). Not a rum base.