Chaetomorpha melagonium is a species of green algae of the family Cladophoraceae.

[1] The attached form is unbranched growing solitary or in a small group to 60 cm long.

The filaments are attached at the base and are stiff and straight.

In colour they are dark green with a glaucus sheen.

Widespread around the British Isles, along the Atlantic shores of Europe, Murman Sea, Greenland, Canadian Arctic.