Genus HypnumGenus HYPNUM, Dill.
The species of the Genus Hypnum in its wider sense all agree in having the peristome double and perfect, the outer of sixteen, strong, lance-shaped, taper-pointed and densely cross-barred teeth; the inner a broad membrane divided to the middle, or about, into sixteen, keeled, yellow segments, distantly cross-barred, entire, or cleft more or less along the keel, the segments generally separated by 1 to 3 filiform divisions (cilia) cross-barred and often bearing tiny spurs on the margin.
The difference in the species will perhaps better be understood by reference to the following synopsis of the sub-genera represented by the species which follow.
Dr. Johnston in speaking of the genus Hypnum said that perhaps it formed one-fourth of the vegetable clothing of Great Britain.
The word hypnum is from the Greek for an ancient name for some sort of moss supposed to promote sleep.