There is a plant well-know for this phenomenon - Verbesina virginica - commonly known as "frostweed". It can produce spectacular ice formations in the right conditions. Here's the best I could do for sample pics using Google images: [HYPERLINK@www.google.com]
I've seen frost flowers from Salvia, Solidago, and occasionally other plants... it depends on the weather conditions. Generally what is needed is mild weather followed by a hard freeze with calm wind.. But V. virginica seems to produce the most spectacular examples.