Some similarities to : Mare's-tail (Hippuris vulgaris), which grows in shallow water, has whorls of wiry leaves which are shorter than those of Horsetails and which belongs to a differing family (Hippuridaceae).
The fertile stems shown in the above photos, taken in Staffordshire, are un-likely to be hybrids, since none occur in the area. However, the infertile photos from Parbold do occur in a region where the hybrid with
- Field Horsetail (Equisetum arvense) to produce
Anglesey Horsetail which only occurs in one hectad of Anglesea.
Water Horsetail (Equisetum fluviatile) to produce Equisetum × willmotii which occurs in but a handful of hectads in the UK.
Marsh Horsetail(Equisetum palustre) to produce Equisetum × font-queri which occurs mainly in Lancashire.
Wood Horsetaill(Equisetum sylvaticum) to produce Equisetum × bowmanii which occurs in only 3 hectads in the UK.
Marsh Horsetail is extant, but it is not known whether or not those photos are of any hybrids.
Uniquely identifiable characteristics
No relation to : Horseradish, Horse-Chestnut [plants with similar names belonging to differing families]
The fertile spikes are without leaves and appear before the infertile spikes bearing whorls of wire-like green leaves. Both stalks and leaves are in sections which, if pulled hard, will part company. Great Horsetail is the tallest Horsetail, and easily recognised by the fawn-coloured long tip of the fertile spike bearing the spores. It is by far the tallest Horsetail, the sterile light-green stems with whorls of wire-like leaves growing to 2m. It grows near water or in damp ground but never in the water as does
Water Horsetail (Equisetum fluviatile).
The branches of the photosynthetic stems are 8-angled [as opposed to 3-angled for
Shady Horsetail (Equisetum pratense); 4-angled for
Wood Horsetail (Equisetum sylvaticum) and for Field Horsetail (Equisetum arvense); 5-angled for
Variegated Horsetail (Equisetum variegatum); and 6- to 7- (up to 10)-angled for
Branched Horsetail (Equisetum ramosissimum)]
The main stems, on the other hand, usually have more ridges: On Great Horsetail they number between 18-40 (up to 60) and are faint grooves.
The horsetails are very primitive non-flowering spore-bearing plants. Like Ferns, such as Bracken, Horsetails also contain Thiaminases which eliminate Vitamin B1 (Thiamine)
from the body, causing disease.
A TOXIC POLYCYCLIC PEPTIDE ALKALOID
Horsetails are poisonous and many contain much the same toxins, such as Palustrine, but in differing proportions. Great Horsetail is more toxic than most, having higher concentrations of the toxins.
Palustrine (aka palustrin) is a polycyclic peptide that can gum up the workings of the normal mammalian body if ingested, such as by sheep, oxen or cows but especially by horses, when the intoxication is then called equisetosis. The characteristic symptoms are breathing disorders, digestive problems and possibly fever. The alkaloids exhibit oxytocic properties, where females can lose their off-spring, which can also happen to pregnant women who consume Horsetail plants.
Marsh Horsetail (Equisetum palustre) has an especially high concentration of Palustrine, hence the name of the alkaloid.
Marsh Horsetail (and possibly other horsetails too) also has derivatives of Palustrine, such as N-FormylPalustrine, N-AcetylPalustrine, Palustridine [N.B. Not Palustridiene, as some sources spell it!] (with the H on the right-most N-atom replaced by CHO) and N-FormylPalustridine. All contain a lactam ring. On alkali fusion Palustrine yields Spermidine.
[There is another molecule with the same common name as Palustrine which is not related in any way to the above]