Lycopus europaeus, commonly known as European water-horehound, is a herbaceous perennial plant belonging to the mint family (Lamiaceae). This species is recognized for its distinctive appearance and its presence in wetland environments across its native range. The plant typically grows to a height of 30 to 100 centimeters, forming erect, square stems that are characteristic of the Lamiaceae family. Its leaves are opposite, sessile or subsessile, and lanceolate to ovate in shape, with serrated margins. The leaf surface is often dark green and can be slightly hairy. During the summer months, European water-horehound produces small, inconspicuous flowers arranged in dense whorls in the upper leaf axils. The flowers are typically white or pale pink, with a tubular corolla and prominent stamens. The fruit is a small nutlet, which aids in the plant's dispersal. European water-horehound is native to Europe, North Africa, and parts of Asia. It thrives in moist to wet habitats, commonly found in fens, marshes, ditches, riverbanks, and other areas with consistently damp soil. While it is well-adapted to its natural wetland environments, it can also tolerate some drier conditions once established. Cultivation requirements generally include full sun to partial shade and consistently moist, fertile soil. It is not widely cultivated as an ornamental plant but can be a valuable addition to naturalistic water gardens or bog gardens. Historically, Lycopus europaeus has been used in traditional medicine. Various preparations were employed for their purported effects, though scientific validation of these uses is often limited. Its ecological role is primarily as a component of wetland flora, providing habitat and food sources for certain invertebrates. An interesting characteristic of European water-horehound is its ability to tolerate waterlogged conditions, a testament to its adaptation to riparian and marshland ecosystems. The square stems are a key diagnostic feature, helping to distinguish it from other herbaceous plants. The plant's common name, water-horehound, reflects its wetland habitat and its resemblance to other plants in the *Marrubium* genus, which are also known as horehounds.