Calliergon giganteum, the giant spearmoss,[1] giant calliergon moss,[2] or arctic moss, is an aquatic plant found on lake beds in tundra regions.

Calliergon giganteum survives in the cold climate by storing nutrients to be used in the formation of new leaves in the spring.

The ground cover of Calliergon giganteum in the arctic has a warming effect which other plants benefit from.

Calliergon giganteum prefers hydric environments, growing best in wet and humid conditions.

For photosynthesis, the optimum water content is 1500-1700% of the moss's dry weight.