This grower is fairly sure of this plant identification.
Chocolate coloured, strong peppermint scent & flavour (some would say after-dinner mint chocolate, but some say Chocolate Cosmos is chocolate scented... I wouldn't!). Combine with Mentha suaveolens (apple mint, also available) for the perfect mint tea (or Mojito - rum and lime not available from this seller!)
Mentha genus (Mint). This genus has about 25 species of aromatic perennial, some of which are evergreen and some semi-evergreen. They are grown for their fragrance, and some for their ornamental appeal.
They are fully to frost hardy, and can grow in sunshine or shade, with rich soil with lots of moisture, but well drained.
Grown for their aromatic foliage, which is both decorative and used as a culinary herb.