Water Mint (Mentha aquatica)

Description:
Short description: water mint - Mentha aquatica (L.)
The corolla is densely short-hairy on the outside.
The inflorescence is terminal, more or less compact, composed of strongly crowded false whorls, whose supporting leaves are equal or shorter than the inflorescences – barely noticeable (and much smaller than stem leaves), and is head-like (rounded at the top) less than 2x as long as wide. There may also appear 1-2 inflorescences from false whorls below the main inflorescence in the axils of upper leaves.
Stem leaves are always distinctly petiolate with 15-25 mm long petiole, possibly short-hairy on both sides or almost glabrous above.
It is a plant 15-50 cm tall with dwarf forms that are leafy in water and grows only on wet habitats, often marshy or occasionally flooded. (not just moist)

Mints from the M. x piperita agg. group (aggregate – group), for example, have inflorescences that are 2-4 x as long as wide. Corolla is glabrous or scarcely hairy outside. Leaves may be glabrous or strongly hairy, petiolate with petiole shorter than 15 mm.

Mints from the M. spicata agg. group have terminal inflorescences that are more than 4x as long as wide and may be compact or several times interrupted, leaves mostly sessile, only lower ones possibly short-petiolate.

Regarding mints with elongate conical inflorescences, which I have already commented on, let me say that mints as a whole are a rather demanding genus for identification, especially the M. spicata agg. group with elongate, pointed inflorescences. Due to great variability within species themselves and numerous hybrids between them, which may or may not be fertile and reproduce vegetatively.
For illustration, they include e.g.: M. spicata; M. longifolia, M. x rotundifolia, M. x villosa, M. suaveolens, M. microphylla ("x" in the name means hybrid), and more could be found.

The next group of mints are those with interrupted inflorescences – composed of false whorls in the axils of stem leaves (supporting leaves of the inflorescence) at the nodes, of which the pennyroyal (or pennyroyal mint) M. pulegium is relatively easily recognizable, having supporting leaves of the inflorescence approximately as large or only slightly longer than the inflorescence. Other mints in this group, including field mint M. arvensis, have supporting leaves much longer than the inflorescences. M. arvensis somewhat stands out, being normally fertile with developed stamens and campanulate calyx barely visibly veined, while others have sterile stamens and calyces with strongly prominent veins.

Description contributed by user Jojoj.

Flowers are not reviewed by experts/botanists, so errors are possible.