Thuidium  Thuidium is a genus of moss in the 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. Members of the genus are characterized by creeping, highly branched, pinnate leaves. There are approximately 230 species found distributed in North America, Mexico, West Indies, Central America, South America, Europe, and Asia.