Well to be more precise this is an old wall. It is about 3 metres high retaining a bank of earth. But it is home to several clumps of fern.
This (and the picture above) are Hart's Tongue ferns, Phyllitis scolopendrium, a European fern introduced into New Zealand and not very common. In Britain you can large stands growing in its natural woodland habitat, but here (in the Dunedin Town Belt) that niche is filled the NZ native Hound's Tongue Fern Microsorum pustulatum. The European Hart's Tongue prefers a limy soil, which is why it is growing on the mortar between the blocks of (probably acidic) volcanic breccia. It also probably accounts fro why it is relatively uncommon in the Town Belt.
I have been unable to identify this fern (and below). I can easily imagine that growing on this wall has stunted its normal growth, making deformed specimens that defy even close identification - sigh!
