Septa numerous, arranged pinnately with regard to four principal septa.
When the division is carried into the second degree, and the pinnae of a compound leaf are themselves pinnately compound, a bipinnate leaf is formed.
The plant is an annual herb with flexuose branches, and alternately arranged pinnately compound leaves, with small, oval, serrated leaflets and small eared stipules.
2) (P. vulgare) is widely diffused in the British Isles, where it is found on walls, banks, trees, &c.; the creeping, densely-scaly rootstock bears deeply pinnately cut fronds, the fertile ones bearing on the back.
Long, the three main branches of which are themselves pinnately divided; it is found in dry, shady places in mountain districts in Great Britain, but is very rare in Ireland.