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..
Succulent plants consisting of a short fleshy rootstock bearing one or several leaves and numerous fibrous often fleshy roots. Leaves erect or pendent, consisting of a simple, palmately or dichotomously lobed, pinnately compound or decompound, sessile or stalked, sterile blade, and one or several separate stalked fertile spikes or panicles (sporophyls), borne on a common stalk. Sporanges formed from the interior tissues, naked, each opening by a transverse slit. Spores yellow, of one sort. Prothallia subterranean, usually devoid of chlorophyl and associated with an endophytic mycorhiza.
Five genera, the following well represented in both hemispheres; the others tropical.
Veins reticulate; sporanges cohering in a distichous spike.
Veins free; sporanges distinct, borne in spikes or panicles.