Mentha arvensis, a
20-60cm tall perennial herb found in somewhat damp places, extend
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 whorls
of 4-5mm long, light purple flowers. Calyxes cut themselves in five,
and the segments pointed. Bloom time: August-October.