Lithothamnion is a genus of thalloid red alga comprising 103 species.

[note 1] The monomerous, crustose thalli are composed of a single system of filaments which grow close to the underlying surface.

Lithothamnion reproduces by means of multiporate conceptacles.

The valid species currently considered to belong to this genus are: The species Lithothamnium calcareum is, besides Tricalcium phosphate, often used as food fortification in plant-based milk substitutes to achieve a similar calcium content as a cow milk which is around 120 mg/100 ml.

[2] However, in April 2021 the European Court of Justice forbade its use in organic food products such as drinks.