Starbucks describes it as a mix of juniper and sage.
On their website, the company says, "Our signature espresso and steamed milk mingle beautifully with juniper syrup. This beverage has a light, pine-like flavor with delightful citrus undertones. We cap this latte with velvety foam and accentuate the remarkable flavor with a dusting of pine-citrus sugar."
You can get one starting Tuesday at participating locations.