Feared by gardeners for their ability to rapidly colonise an area and smother other plants, the horsetails are in fact a living fossil, remarkably similar to the early plants that made up the vast swamp forests of the Carboniferous era. One of the SAPS 'Star Plants' for your lab, showing evolution in action to get your students thinking. With sympathetic ground staff, these are well worth keeping (securely) in your school.

Practicals

• Evolution - These can be used alongside fossils (real or facsimiles) of early land plants to teach plant evolution. The University of Cambridge has produced a thought-provoking evolutionary timeline to use with your students. A good alternative to another ‘living fossil’, the ginkgo tree.

Teaching Topics

• Evolution
• ‘Living Fossils’

Description

Common Horsetail, Equisetum arvense

Our modern horsetails are invasive weeds, with fast growing rhizomes (underground stems) and roots that go down up to 2m. However, they are 'living fossils' - closely related to the Calamites trees that made up the giant swamp forests of the Carboniferous period. The Calamites looked remarkably similar to our modern horsetails - but 18-27 metres tall. Their specialist adaptation to swamps meant the Calamites and other plants, such as the tree-sized club mosses, died out when their swamp habitat dried up, and are left to us in the fossil record. They disappeared at the end of the carboniferous period but left living fossils in our modern horsetails and club mosses.

Horsetails have a very distinct structure and separate vegetative and fruiting stages. They are a remarkably efficient coloniser and use rhizomes that spread horizontally across the soil; a strategy that has not changed from their ancestors. The epidermis contains silicates, which in their earlier form had proved a challenge for the herbivorous dinosaur, Iguanodon.

Growing and sourcing

Adapted to: Swampy forests

Obtaining: You may find these growing as invasive weeds in your school grounds. If not, cultivars can be purchased from specialist plant nurseries online.

Care: These plants require little active horticulture, and are best kept outdoors. As these are EXTREMELY good colonisers, they must be kept in large pots, and never planted in the open ground. They prefer continuous moisture, so a pot that has no drainage hole is best suited to these plants. Keep them in a semi-shaded area. During dry spells, water once a week.

Images