This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Terrestrial, annual or perennial, moss-like plants with branching stems and scale-like leaves, which are,many-ranked and uniform, or 4-ranked and of two types spreading in two planes. Sporanges 1-celled, solitary in the axils of leaves which are so arranged as to form more or less quadrangular spikes, some containing 4 megaspores (megasporanges), others containing numerous microspores (microsporanges), which develop into small prothallia, those from the megaspores bearing archegones, those from the microspores antherids.
The family consists of the following genus: