Dino-botany in Andover

Rooksbury’s Dinosaurs

David Beeson

Best time to visit is late spring or summer.

If you enter the Rooksbury Local Nature Reserve from the old Test Valley railway line and soon turn right you will spy a miniature forest of horsetails on your right. They grow up to 60cm in height. Their relatives were around with T. rex and Stegosaurus. Forests of tree-like horsetails were the food of many dino-herbivores and when they only partly decayed after death, they donated us coal. (Of course, flowering plants such as oak trees had yet to evolve.)

For over 100 million years horsetail relatives dominated the understory of late Paleozoic forests. Some of these plants were large trees reaching to 30 m (98 ft) tall.

The most striking feature of our horsetails (Equisetum is the scientific name of the genus) is the whorl of green branches arranged one above another up the stem. The plant’s minute leaves are located where these branches join the main stem – a ring of fused miniature leaves that is easy to miss.

Being green, the stems and branches are photosynthetic and trap sunlight energy to drive the plant’s chemistry.

I’m told that during World War Two German’s were send out into the fields to collect horsetails for the war effort. What they were used for is unknown to me*.

Horsetail stems are abrasive as they contain sandy silica (SiO2) and this makes them feel like Brillo pads. This silica would have worn down the teeth of the dinosaurs and is still a deterrent to grazing animals.

Horsetails, like mosses and ferns, are non-flowering. The tall plant we see growing in this soggy part of the reserve produces spores from cones. These spores germinate to form miniature structures that make eggs and sperm. When these gametes join the resulting embryo can grow into the big horsetail that we see.

So, like the other non-flowering plants there are two distinct stages to the plant’s life history – called Alternation of Generations.

There are relatives of the horsetails found elsewhere in the UK. Club mosses are sometimes encountered in the New Forest and in mountainous areas. Yet, there is one place you might encounter them which is slightly unexpected – garden centres. A small club moss called Selaginella is sold as a house plant. In the wild I’ve found it in diverse spots such Southern Italy and West Wales.

Gardening tip. Horsetail is an invasive, deep-rooted perennial weed that will spread quickly to form a dense carpet of foliage, crowding out less vigorous plants in beds and borders. Best keep it in a wild part of the garden.

A plant (Hippuris or mare’s tail) that looks similar to a horsetail, but grows in water, is unrelated – being a flowering plant.

Some, overseas cultures, are known to eat* young stems and to use it in traditional medicine (Unproven). The stems are said to taste rather like asparagus. However, the plant is said to be poisonous to horses … so, I’m NOT trying it!

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