You may not realise it, but your garden or local park might shelter prehistoric relics. The coarse, bristly stems of field horsetail are a common feature of damp grassy places, especially on sandy soils.
They’re seldom popular with gardeners, because of their tendency to spread – but as members of a group that has thrived unchanged for more than 300 million years, they deserve respect.
In spring, among the lurid green bog-brushes of this plant’s normal growth, you’ll also find even weirder-looking reproductive stems. These lack green pigment and are topped with cones (more correctly strobili) bearing the spore-producing structures, or sporangia.
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At about 0.05mm across, individual spores are too small to admire even with a hand lens, but what you’d see with the help of a microscope is remarkable.
Each spore can ‘walk’ and ‘jump’ using four ribbon-like structures called elaters. These start out wrapped around the spore but unfurl as they dry out, thrusting the spore in a random direction, then curling up again as humidity increases.
The process is repeated in response to subtle fluctuations in humidity, such as those that are caused by a period of sunshine and shade or by gentle air movement. Every now and then, the elaters snag on each other, building up elastic tension until they spring apart suddenly, propelling the spore up to 1cm into the air.
These jumps are more than enough to catch a well-timed breeze and send the spore on its way. However, unlike the explosive dispersal of some flowering plant seeds, which is usually an all-or-nothing splurge, the walking steps and jumps of horsetail spores can be repeated many times.
So while it all happens on a micro scale, given time and favourable conditions it’s a highly effective dispersal mechanism. The plant must be doing something right – it’s been reproducing that way since the Palaeozoic era.
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