Can Saxifrages really break rocks?

Quite often we are asked whether Saxifrages can split open crevices in the rocks in which they live.  The answer is no!

The only rocks Saxifrages were ever meant to split were in fact kidney stones, and this was itself based on a fallacious medical superstition. It is true that many books do explain the name by allusion to the fact that various species grow in rock crevices, and suggest that the roots actively split the rocks by expansion, but the real explanation is deeper and more interesting than this.

The name Saxifraga does indeed mean breaker of rocks, and dates back to Dioscorides, the Greek herbalist of the 1st century. It next crops up in the herbals of the Middle Ages accompanied by a picture of Saxifraga granulata, and this is the only species known by this name in the 16th century.

This plant actually grows in wet meadows, not on rocks. The species that grow in rocks were either undiscovered or mainly known as stonecrops until Linnaeus circumscribed the modern genus Saxifraga in 1737.  The type species in the genus is S. granulata.

The reason a meadow plant got to be called stone breaker was because it has small grain-like bulbils at the base of its stem, coupled with kidney shaped leaves. In herbalism there existed for centuries the so-called "doctrine of signatures", whereby the shapes of plant parts were interpreted as hints placed by God to their suggested medicinal uses. This form of magic dictated that this plant was a sure-fire cure for urinary calculi, or kidney stones.

It is very doubtful that any true species of Saxifrages have any real medicinal value. Several unrelated plants like the Umbellifer Pimpinella saxifraga (Burnet Saxifrage) and Petrorhagia saxifraga (Tunic Flower) also have inherited the same name through a herbalist connection.

As for the alpine species that grow in rock crevices such as S. tombeanensis, well, they just exploit existing cracks. Like many other saxatile species, they may send roots many metres deep to seek water and minerals, but there is no scientific evidence I am aware of that such plants actually widen the crevices significantly.

I'm guessing now, but a single over-imaginative author at some stage has tried to explain the name Saxifrage in this way. This factoid has then become repeated in subsequent books as a proven truth, and incorporated into folklore and even artistic metaphor as a powerful meme.
 

Paul Kennett