This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Rootstock with fleshy fibrous roots. Frond oblong-lanceolate, with a simple fertile spike attached to it, much in the way of the spathe and spadix of the Aroideae. Spore-cases confluent, globose, arranged in a distichous spike. There are about four widely-distributed species. Name from a snake, and
a tongue, in allusion to the fertile spike.
1. O. vulgatum. Adder's Tongue. - This curious little plant is very distinct from all other Ferns. The single frond is from 3 to
9 inches high, with a blade from 2 to 4 inches long, and varying from ovate-oblong to lanceolate. There are two forms - vulgatum proper, with ovate fronds and long fertile spikes; and Lusitdnicum, with narrow lanceolate fronds and spikes lesss than an inch long. The former is not uncommon in pastures and woods, and it is also common in the temperate regions of the north and south.