Michaelmas Herb

I was wondering if you knew the herb that is associated to Michaelmas Day (the holiday for the Archangel Michael). It's for a research project.

Several asters are known as Michaelmas daisy. According to Hortus Third, at least four species go by that name, including the New England aster (Aster novae-angliae) which we carry.
Although asters are not generally regarded to be herbs, we note that they do indeed have medicinal properties. The native Americans used New England aster for fever, catarrh and pain, and the Iroquois in particular used it as a 'love medicine'. Was it an early herbal 'Viagra', we don't know.