You may not know it, but your garden or local park could be hiding something from prehistoric times. The rough, hairy stems of field horsetail are a common sight in damp, grassy places, especially in sandy soil.
Gardeners usually do not like this plant, because it spreads so easily. But it belongs to a group of plants that has stayed almost the same for more than 300 million years, so it deserves some respect.
In spring, along with the plant's normal bright green stems, you will also see stranger-looking stems used for reproduction. These stems have no green color. Instead, they have cone-shaped tips that hold small structures, which produce spores.
Each spore is only about 0.05mm wide, far too small to see clearly even with a magnifying glass. But under a microscope, something amazing appears.
Each spore can "walk" and "jump" using four thin, ribbon-like parts called elaters. At first, these parts are wrapped tightly around the spore. As they dry out, they slowly unroll and push the spore in a random direction. Then, as the air becomes more humid again, they curl back up.
This happens again and again as the air around the spore slightly changes, for example when the sun comes out or goes behind a cloud, or when there is a light breeze. Sometimes the elaters catch on one another. This builds up tension, until they suddenly spring apart and shoot the spore up to 1cm into the air.
These small jumps can be enough for the spore to catch a passing breeze and travel further. Unlike the seeds of some flowering plants, which burst open all at once and only get one chance to spread, horsetail spores can walk and jump many times.
So even though it all happens on a tiny scale, given enough time and the right conditions, this is a very effective way to spread. This plant must be doing something right, since it has been reproducing this way since the Palaeozoic era.