[3] A very useful defining characteristic of Hypnum mosses are their leaves which are often falcate-secund (meaning that they are sickle-shaped and point to one side of the plant).

[3] Growth forms of Hypnum mosses vary from creeping to erect.

[5] Leaves are secund or falcate-secund, broadly to narrowly ovate, and can be plicate.

[3] Alar cells in the leaf bases are typically differentiated and range in shape from hexagonal, triangular, quadrate, or sub-quadrate.

[3] The outer surface of exostome teeth have zigzag lines as well as lamellae.

[3] The annulus is either 1-3- times seriate or has very minimal amounts of cell differentiation.

[3] Spores produced by the sporangium are round and can be smooth or papillose in texture.

[3] In terms of sexual reproduction, Hypnum mosses are autoicous, dioicous, or phyllodioicous.

[3] Historically, Hypnum mosses were used to stuff bedding because they were falsely believed to have sleep-inducing properties.

[6] The CityTree air filter, present in many European cities, uses Hypnum to capture and consume pollutants.