Roots of plants are known for being able to pierce through the firm soil and even solid stone to some extent. However, it occurred to me recently that I might be overestimating this ability as soil isn't the continuous material it seems from a large scale, but rather it is made of many small but firm granules connected by softer organic material which got me wondering just how important the granulation of soil is.
Typically, I don't see large stemmed plants growing out of solid rock despite that many granules of soil have a similar hardness to solid rock. But, could a plant that normally grows in soil grow instead in solid rock under the right circumstances? Soil is granulated, whereas solid rock is not.
I'm no expert, so I can only imagine different possible scenarios.
Could a large solid rock support a large and stemmed plant if it was porous enough? In other words, is it unimportant that the rock is very firm so long as there is enough exposed surface area to allow the chemical reactions that take place during the ion exchange at the roots and possibly break down the stone?
Or alternatively, it may not even be the porous or granule nature, but it might simply be the solution water carries. Could an large plant grow off of a large and smoother solid stone alone with roots rested near the base, but, if there was water running fast enough and warm enough to dissolve the surface of the rock and allow the ion exchange to take place in roots once the water was carried downstream to those roots?
Perhaps it's neither of those possibilities and it is solely the ability of a plant to anchor itself that matters the most in this issue. Even if a plant could pierce through the stone with its microscopic roots, since its stem also grows proportionately, if a plant can't anchor itself then it will just be blown away or washed off, so only small plants can anchor themselves to rocks.
Which of these traits is the most important factor in why plants don't typically grow out of larger solid rock, and can it be overcome to successfully grow large stemmed plants out of large solid rock?