Up until that moment, I’d been intending to make some kind of very standard beer style—an IPA or a porter—and simply substitute yarrow for the usual hops.
experimental beers with a botanical twist
Not the citrus fruit but the North American wildflower Monarda fistulosa, also known as purple beebalm or Oswego tea. Minty, but not strongly so; its name is due to an imagined resemblance to the aroma of the bergamot orange. The Wikipedia says “Although somewhat bitter due to the thymol content in the leaves and buds, the plant tastes like a mix of spearmint and peppermint with oregano.” The Lady Bird Johnson Wildflower Center website has a good run-down of its medicinal uses, gathered from several sources.