A horsetail is a type of ancient plant that looks like a bundle of green, jointed tubes topped with thin, hair-like branches, somewhat resembling a horse's tail, which is how it got its name. These plants grow in wet areas like marshes, stream banks, and ditches, and they feel rough to the touch because they contain silica, a gritty mineral that's also found in sand and glass.

Horsetails are living fossils. Their ancestors towered as tall as trees over 300 million years ago, forming vast prehistoric forests. Those giant horsetails lived long before humans appeared. Today's horsetails are much smaller, usually just a few feet tall, but they're survivors that have barely changed in millions of years.

You might spot horsetails growing in clusters near water, their green stalks standing straight up like little bottle brushes. Early American settlers used dried horsetails to scrub pots and pans, calling them scouring rush because the silica made them work like natural sandpaper. The plants spread through underground stems that are notoriously difficult to remove, which is why gardeners often consider them stubborn weeds. But to a paleontologist or naturalist, each horsetail is a glimpse into Earth's ancient past, still thriving in the modern world.