This species needs only cracks in the rock to establish itself. The seeds are dispersed by ants. Cymbalaria muralis grows along the coast in southern Norway and is used as a garden plant.
Moreover it does not need cracks...or rocks at all. It's currently smothering an Opuntia in my C&S bed. It is best in walls where it has been very reliable. It shows up in pots and moves itself around where it likes. My favorite plant of it was growing in a crack in a stucco wall of a building---no soil at all and returns every year.
Carlo A. Balistrieri
Carlo Balistrieri Photography
Lake City, SC
Doesn't appear hardy in my area.
St. John's, Newfoundland, Canada
1800 mm precipitation per year
I must remember to take a picture of my colonies tomorrow: I've finally isolated it in a few spots where it can't do too much damage, but I can enjoy it's Kenilworthian charms!
For every minion of the peaks there are a dozen steppe children growing in the dry Continental heart of all hemispheres still unknown to horticulture.