Cymbalaria Species, Mini Kenilworth Ivy, Pennywort

This is attractive on old rockwork and stone walls. The flowers are very pretty but require close inspection---this is grown mainly for i...Read Morets tiny attractive foliage.

This can spread just as aggressively as C. muralis, but it's much lower---under an inch tall---and (I suspect) less inclined to overwhelm other perennials in the garden. Personally, the jury's still out, but it can hardly be any worse than C. muralis.

It can be hard to tell whether this plant is truly perennial or simply returning from seed. But it returns reliably in my garden in Boston Z6a, and I understand it can be reliable as far north as Calgary Z3.