Like some other small ferns, Wall-rue Asplenium ruta-muraria is probably entirely confined to brickwork and stonework in Norfolk. It is widely scattered but thinly spread. Old railway bridges, churches and old garden walls are all good hunting grounds.
Updated January 2019. Lime green circles and orange squares: 1987-1999 Green circles and dark red squares: 2000-2019
There are still nine 10km squares where wall-rue is yet to be re-recorded and it may well be hiding away in isolated locations in the remaining squares where it wasn't recorded for the 'A Flora of Norfolk'