Cactus in the Boundary Waters?

The hoarfrost on the trees looked like cactus to me. Hoarfrost? Where on earth did that word come from? It sounds so odd. It’s Old English according to Dictionary.com,  “expressing the resemblance of white feathers of frost to an old man’s beard.”

Why did we have hoarfrost on the trees? I knew it had something to do with moisture in the air…

According to Weather.com “Water vapor in the air over cold ground with a surface dew point at least as cold as 32 degrees. The water molecules contact a subfreezing surface and they jump directly from a gas state to a solid state leading to a coating of tiny ice crystals. ”