Spearmint is a family and a genus, so the difference in appearance is small, but the smell is different. Spearmint has a relatively fresh smell, which is not so strong, cool, and not very pungent.
The fragrance of peppermint should be strong. If you smell it close, you will feel it is blunt and pungent. You can tell it from this point
The former leaves are smaller in shape and about 4-5cm in length. Its leaf color should also be darker, the texture on the leaf is more clear and obvious
The latter leaves larger than the former, about 2.5-7 cm in length. The color of its leaves is lighter, and the texture on it is not so clear.
The former flowers are purple or white.
The latter flower color is mostly cyan purple or lilac.
In comparison, the height of the former plant to be short, about 40 - 130 cm.
This latter kind of plant is relatively tall, the height of the plant is about 40-150 centimeters.