What is waxy petals sprouting' from bathroom tiles?

It could be a shelf fungus, indicating rotten wood behind the tile.

Here is a link to a google image search.

google.com/images?hl=en&client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&um=1&q=shelf+fungus+&btnG=Search+Images">http://images.google.com/images?hl=en&client=firefox-a&rls=org.mozilla%3Aen-US%3Aofficial&um=1&q=shelf+fungus+&btnG=Search+Images