Calliergon cordifolium is a species of moss in the Amblystegiaceae family commonly known as the calliergon moss (though this name refers to the genus Calliergon generally) or heart-leaved spearmoss. The species is abundant in the right habitat, and grows in marshes and wet woodland, especially woodland of alder (Alnus) or willow (Salix), as well as around streams, ditches and pools. The species grows in tufts among other moss species. Calliergon cordifolium requires a wet environment to grow, and often grows completely submerged in water. It typically prefers lowland, but has been recorded as high as 910 metres (1,000 yd) above sea level in Inverness, Scotland. The species has a circumpolar Boreo-temperate distribution. It is found throughout Europe (including north, into the Arctic Circle