I always mentally referred to these icy extrusions as frost flowers, but had never read anything about them.
Inspired by my friend Travis’ success just Googling the word or phrase that comes to mind, I tried typing frost flower in the search field… Guess what? These structures are commonly referred to as – frost flowers! They also have a scientific name, apparently: Crystallofolia. This website was particularly detailed: http://w3.biosci.utexas.edu/prc/VEVI3/crystallofolia.html