Horsetails: relic plants from prehistory
by Dave Walker, UK
(Please note: this article celebrates the attractive features of horsetails from the perspective of a UK amateur naturalist but does not offer any help on their eradication. The following Google search will list a wide variety of advice for different areas of the world www.google.com.)
If
the hero in H. G. Wells' story 'The Time Machine' travelled back
ca. 350 million years, he couldn't fail to notice horsetails as
he stepped out of the machine into a steaming swamp. The
horsetails would have been a dominant part of the vegetation with
magnificent specimens reaching 30m or more in height and 1m in
diameter.
Unfortunately the common horsetail plants of today are much smaller than their prehistoric relatives and it's only the fossil record that provides a glimpse of their heyday.
Horsetails don't have flowers to attract the attention or showy leaves like ferns, but nevertheless they are attractive plants with interesting macro and microscopic features.
The image right shows a horsetail (ca. 0.3m tall) in one of its typical habitats i.e. in the partial shade growing amongst the understorey of a damp wood edge. (The central plant with pale green stem and whorls of branches). It's easy to see why they are often overlooked, as many of the common species are barely taller than the surrounding grasses. Depending on the species, they grow in habitats such as roadsides, stream banks and salt flats.
In urban areas away from nature reserves, the species found are likely to be common, so it's worth studying them in situ with a 10X hand lens and if possible bring home the top half of a stem with a whorl of branches for closer inspection.
The whorls of branches (see left below) are very attractive in some species, especially those of the wood horsetail (Equisetum sylvaticum) which resembles a miniature Christmas tree. The green whorls aren't actually leaves; the leaves in horsetails are reduced to sheaths which clasp the stem (see images below).
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 Detail of base of a clasping leaf |
 Detail of upper part of a clasping leaf. |
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A cross section of the jointed stem is worth
looking at as they are ridged with hollow centres; features which
are useful diagnostic clues to identify the species. Just a crude
cross section 1mm thick when viewed with a hand lens or stereo
'scope will show the detail shown right.
There are only ca. thirty species of horsetails in the world which are all in the genus Equisetum (Phylum Sphenophyta). In the UK there are only eight or so species, but despite this they are not always easy to identify, as they form hybrids and their characters are variable. In the UK an excellent guide to identifying horsetails (and ferns) is reference 1.
Some species
produce two kinds of shoots, one vegetative and another bearing a
cone called the strobilus (shown left). When ripe this cone
releases tiny spores. These cones don't last very long, but if
you find a horsetail with just ripening spores, collect some
spores and study under the microscope. As they dry they have
hairs wrapped around each spore called elaters which uncoil and
help distribute the spores. This phenomenom seems a neat
subject for the enthusiast of video microscopy, if you've
captured any footage of spores and would like to share it let me know.
Horsetails (also known as the scouring rush) have been used for scouring pans and polishing, as the epidermal cells in the stem contain silica which make them abrasive. They are poisonous to livestock although they have been used in some folk medicines. (Addition: I had an interesting email from a reader who told me that his geese loved eating horsetail plants, which suggests they are not poisonous to all farm animals!)
If you have the facilities you may like to try preparing your own stained plant sections to study cellular detail, although their silica content may make this trickier than for other plants. I'm fortunate to have a set of sections prepared by an accomplished UK slide maker called John Nicholls.
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So if you haven't studied horsetails before, it's worth keeping an eye out for them, as they are fascinating plants and in their own way are as attractive as the more commonly studied and admired flowering plants.
General comments to the author Dave Walker welcomed. But please don't ask me how to eradicate them. Try a keyword search like 'horsetails' with 'eradication' on eg www.google.com. The best advice may vary depending on which country you are in.
The author is an amateur naturalist. In-depth information on horsetails can be found via web search engines or visit brittanica.com where Encyclopaedia Britannica entries are complemented by links to online resources.
Footnote
There are some exotic horsetails with heights approaching their prehistoric forebears. E. giganteum is a South American species 10m tall (2cm diameter) which is supported by the tall vegetation surrounding it.
References
1) 'The Fern Guide'. A field guide to the study of ferns, clubmosses, quillworts and horsetails of the British Isles. By J. Merryweather and M. Hill. Field Studies Council, 1995, 2nd Edition.
2) Encyclopaedia Britannica, 15th edition, 1993.
Pictures were all taken by the author.
Published in the June 1999 edition of Micscape Magazine.
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