1 Blechnums and Polypodiums
There are two groupsí ferns that you are likely to find in a British garden, which have fronds with simple lobes down each side of the main stem. They are members of the groups (genera) Polypodium or Polypodies and Blechnum or Hard Ferns. They are fairly easy to tell apart. Because Polypodiums differ from most ferns, in always having a spreading habit, which makes them form irregular clumps, in fact polypodium means many footed. The only Blechnum with this habit is Blechnum penna-marina, or the Pen Of The Sea which is not common in gardens, and easy to tell apart. (see below). Polypodiums are also easy to distinguish, because they grow rather upright and are rarely more than 30cm 1foot high. In addition they often show in late summer clusters of sporing bodies, like little pin heads on the frond back, yellow or orange in colour when ripe, and without a cover over them of the kind found in most ferns. Unfortunately polypodiums are a large and complicated group and it is not possible to go into specific types here.
Of the Blechnums or Hard Ferns, the one most likely to be found in your garden is the British native hard fern, Blechnum spicant. This is easy to tell from the polypodiums, as it forms a roughly round crown, like most larger ferns, that is to say with all the fronds radiating out from the centre. It also only grows on neutral or acid soil, and often has two different types of frond, with the fertile spore making fronds, coming up as a very upright ring, in the centre of the other fronds. There are a number of other foreign Blechnums sometimes grown in our gardens; but only B. penna-marina is common. This is a small spreading fern rarely more than 15cm/6 inches high, with glossy green fronds, which make it difficult to mistake for any other fern.