Thuidium is a genus of moss in the family Thuidiaceae.

The name comes from the genus Thuja and the Latin suffix -idium, meaning diminutive.

This is due to its resemblance to small cedar trees.

[1] Members of the genus are characterized by creeping, highly branched, pinnate leaves.

[1] As of October 2024[update], World Flora Online accepts 55 species, along with 147 synonyms and 5 unplaced:[2]