It's bad news when these appear in your garden. This is the spore-producing shoot of field horsetail Equisetum arvense, about to liberate thousands of spores which have a unique adaptation to aerial invasion, which you can see by clicking here.

Once it's established this plant is well-nigh impossible to eradicate. Its underground stems (known as 'devil's guts') run deep and fragment easily, regenerating new plants just when you think you've dig it all out. Still, it could be worse; back in the  Carboniferous, 300 million years ago, when the coal measures were laid down, these grew 10 metres tall. 

Living fossils

I found these strange, spore-producing shoots of field horsetail Equisetum arvense on a grassy bank near Durham city this afternoon. Known as the 'devil’s guts' to gardeners, on account of its devilish creeping underground rhizomes and resistance to herbicides that together make it almost impossible to eradicate, it produces this yellowish spore stalk first and green shoots only after these have shed their spores and withered away. Field horsetail grows to a height of around 30cm., but back in the Carboniferous, about 300 million years ago, plants that were 10 metres tall but otherwise identical flourished in steamy primaeval swarms. Like present-day horsetails, these gigantic ancestors’ stems were rich in silica and so were slow to decay, leaving excellent fossils whose basic features are almost identical to those of their present-day descendants. When I tapped the sporangia pictured here they release clouds of spores that drifted away on the wind......and if you want to see what these remarkable spores look like visit this post on my other blog, Beyond The Human Eye