Species in the genus Mentha:

Mentha arvensis / Hakka ハッカ

Mentha arvensis, a 20-60cm tall perennial herb found in somewhat damp places, extends many long rhizomes to propagate, with vellus hairs on stems, leaves, and calyxes. The leaves are opposite, 2-8cm long, 1-2.5cm wide, in a long oblong shape, with pointed tips, margins sharply serrated, and backsides with glandular spots. Axils on the upper parts put 4-5mm long whorls, light purple flowers. Calyxes cut themselves in five, and the segments pointed. Bloom time: August-October.