Bryum richardsii is a medium-sized species with a strongly developed leaf border, denticulate to sharply serrate leaf margins, and evenly foliate to weakly rosulate stems. Its most distinctive feature is presence in the axils of the uppermost leaves of numerous long, slender branchlets that have scale-like leaves. There are three other rosulate Bryum species in Central America (B. canariense, B. leptotorquescens, and B. billarderi) that could be confused with B. richardsii. Bryum canariense differs from it in having short, thick‑walled leaf cells and a scarcely differentiated leaf border. Bryum leptotorquescens differs from B. richardsii in having a weakly developed leaf limbidium, serrulate leaf margins, and a pseudautoicous sexual condition. Bryum billarderi has strongly rosulate plants and further differs from B. richardsii in its non-decurrent leaves, serrulate to serrate leaf margins, and the presence of papillose propagula in the upper leaf axils.

When the rosulate habit of B. richardsii is nearly lacking it might be confused with B. densifolium. Bryum densifolium is a larger plant (20–70 mm high) than B. richardsii with flexuose to loosely twisted leaves, margins often doubly toothed, and somewhat longer leaf cells.