Northern Giant Horsetail

Equisetum telmateia subsp. braunii

This is an annoying and neat plant all at the same time. It's spores often hitch a ride in your compost or wood chips and it can be *extremely* difficult to eradicate from your garden once it's established, but the fascinating thing is that it is a living fossil. Horsetails are the only remaining genus of the class Equistophyta which go back to the Devonian Period - that's somewhere in the neighborhood of 400 million years ago!