The Gelidiellaceae is a small family of red algae containing 5 genera of agarophytes.

[2] Gelidiella acerosa is found worldwide, from Europe, North America, Central America and South America, the Atlantic Islands, Africa, Indian Ocean islands, South west Asia, Asia (including China, Japan and Taiwan), South-east Asia (including Vietnam, Myanmar, Thailand, Singapore, Philippines and Indonesia), Australia, New Zealand and the Pacific islands.

[5] In 1987, Maggs and Guiry thought that the family should be merged with Gelidiaceae, but this was mostly ignored by later authors.

[9] Agar can be derived from many types of red seaweeds, including those from families such as Gelidiaceae, Gracilariaceae, Gelidiellaceae and Pterocladiaceae.

It is a polysaccharide located in the inner part of the red algal cell wall.