Adder's Tongue Fern has a spore-less oval leaf-blade that is blunt and has no midrib. It also has a narrow pointed spore-bearing spike on a stalk. The spike has from 10 to 40 segments on each side. Told from Small Adder's Tongue Fern by nearly all the fronds arising singly rather than 2-3 together. It grows from a rhizome base and is usually 10 to 20 cm tall, rarely 30 cm.

This small, hard-to-spot plant occurs singly in un-improved pastures, old damp meadows, rock crevices and grassy path-sides but also occurs in colonies of hundreds of plants in sand dune slacks.

Spores ripe from May to August.

Perennial.

Occasional but fairly widespread in lowland areas of Britain it can occur in good numbers in a few suitable areas.

Occasional and local in Leicestershire and Rutland. In the 1979 Flora survey of Leicestershire it was found in 70 of the 617 tetrads but has decreased in numbers since then.