Some similarities to : Wall-rue (but that has leaflets that are rounder and in three's)and Maidenhair Spleenwort (but that has leaflets that are in opposite pairs and is more delicate than Rusty-back) and to Green Spleenwort (which although it has in alternate leaflets, they are attached to the mid-rib at a point rather than along their length) or the Polypodys (but they are much larger). All these lack the rusty-brown scales on the back of Rusty-back.

Uniquely identifiable characteristics

Distinguishing Feature : The rusty-coloured scales on the back.

There is a very definite preference for Rusty-back in the South-West of the UK and a definite avoidance of the North-East. It prefers lime habitats, either cracks in limestone dry-stone walls, or mortar cracks in walls, but also grows in limy rocks.