Lyngbya majuscula is a species of filamentous cyanobacteria in the genus Lyngbya. It is named after the Dane Hans Christian Lyngbye.

As a result of recent genetic analyses, several new genera were erected from the genus Lyngbya: e.g., Moorea, Limnoraphis, Okeania, Microseira, and Dapis. Several specimens identified as L. majuscula and collected in marine tropical regions are now classified as members of the genera Okeania and Moorea.

L. majuscula is the cause of seaweed dermatitis.

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