300 Million year-old Survivors

These are the fertile shoots of great horsetail Equisetum telmateia, photographed along the Long Walk at Howick on the Northumberland coast last weekend. Each one of those small polygon-shaped objects in the cone-shaped head releases hundreds of spores. You can see some micrographs of spores from a similar field horsetail here. Horsetails are the last living descendants of a group of plants that flourished back in the steamy Carboniferous swamps, 300 million years ago, when the coal measures were laid down. Carboniferous horsetails, classified in the genus Calamites, were essential similar to their living descendants but much larger, some reaching 10 metres in height. As soon as the fertile shoots of great horsetail have shed their spores they wither away, but by then the green vegetative shoots of this year's plants will have begun to elongate and will eventually form dense one metre-tall thickets of stems - minute compared with their extinct ancestors, but still impressive.

Here be Giants

This dense forest of great horsetails Equisetum telmateia thrives on the low cliffs and dunes that flank Warkworth beach in Northumberland, but if you could time-travel back to the Carboniferous 300 million years ago, when the coal measures were laid down, you’d see plants that looked very similar. The first amphibians that emerged on land would have slithered between their stems. Today’s horsetails are living fossils – the last few survivors of a group of plants that were once a diverse and dominant component of Earth’s vegetation, thriving in steamy swamps thanks to air channels in their stems that conducted oxygen to their roots and allowed them to survive in stagnant mud. Fossil horsetails from the Carboniferous are common in coal deposits and are virtually indistinguishable from their present-day counterparts – except that those ancient horsetails were true giants of tree proportions, sometimes up to thirty metres tall. Our great horsetail can’t match that – a couple of metres is about the limit of its growth. Horsetails have very distinctive whorls of long , thin leaves at nodes along their grooved, circular stems. They contain large amounts of silica, which gives the dried plant abrasive properties and accounts for its other common name – scouring rush.