Eriophorum, or cotton grass, is a genus that contains about 25 different sedges. Though it may resemble a grass, it technically isn't. Where grasses have leaves that are alternately arranged in pairs of two, sedges typically have sets of five triangular leaves that are spirally arranged. Cotton grass can be identified by the fluffy, white cotton-like substance in which its seeds are wrapped. The various species of Eriophorum are widely distributed throughout the Northern hemisphere, with an especially large presence in higher latitudes.
The cotton-like balls that give these grasses their name perform a similar botanical function to true cotton. Like true cotton, the fluffy masses are grown around seeds. When it comes time for the seeds to fall and disperse, the light material can help the seed heads to be carried off on the wind. This allows them to spread farther from the parent plant than might otherwise be possible. In addition to reproducing by seed, many species can reproduce clonally through the spread of a rhizome mat under the soil.
Species of Eriophorum, such as common and hare-tail cotton grass, can be found throughout the northern parts of Asia, Europe and North America. They grow well in the acidic conditions found in and around bogs and marshes. Common cotton grass can be identified by flowering stems that grow to about 28 inches (70 cm) and bear up to five seed heads in the form of cotton-like masses. The multiple seed heads per stem leads this plant also to be known colloquially as multi-headed bog cotton. The hare-tail variety can grow to about 24 inches (60 cm) and usually forms tussocks that are punctuated by taller flowering stems that each bear a single, cottony seed head.
The Arctic species commonly grows well in high northern latitudes, while slender cotton grass proliferates across North America, Asia and Europe in the boreal region just south of the Arctic region. Arctic cotton grass typically bears only a single seed head per stem and can provide a valuable food source to certain migratory birds and even large mammals such as caribou. The Inuit people also have used the fluffy seed heads as candle wicks. The slender type also bears a single seed head per flowering stem, though it often spreads through an underground rhizome mat instead of growing new plants from seed.