A select few of our present-day weeds are descended from much grander primeval forms. Field horsetail (Equisetum arvense L. #3 EQUAR) and related specie, are "degenerate" herbaceous plant, whose tree-sized ancestors dominated forests in the Carboniferous period about 300 million years ago. Indeed, early equisetums contributed significantly to the formation of coal beds (12). The reproduction of the equiseturns partly explains their general extinction. Spores in the plant's small fertile cones produce two tiny gametophytes which bear male and female organs; they are independent of the plant and each other. Passage of sperm from the male to female organ for fertilization can occur only in water. When the union occurs, a zygote develops and the resulting embryo produces both a green sterile bushy shoot-the most conspicuous horsetail form-and a brown fertile one. A land plant that depends on water for its reproduction has some obvious technical disadvantages. Changes in climate and geography late in the Paleozoic favored true dry-land plants such as the new conifers and cycads. The giant equisetums disappeared and the present "living fossils" are relegated to restricted areas (12). This miniature relic of the Age of Amphibians is a survivor in every sense of the word and will appear in the most inhospitable places (3).
Equisetums are not only native to North America, where they range from Greenland to Alaska and southward from Virginia to California, but they are also indigenous to Europe, including the British Isles (5). Most of the species are native to the northern temperate regions. One typical northern species, marsh horsetail (E. palustre # EQUPA), is found from Newfoundland across the northern U.S. and Canada into Alaska, making locally abundant stands in wet meadows and on margins of streams and ponds (13). Horsetails thrive in moist grasslands and on damp road embankments, especially on sandy or gravelly soils (5); they prefer acid soils (13).
The horsetails are primitive perennial plants, reproducing by spores and deep, tuber-bearing rhizomes (13). In early spring large colonies of the fertile horsetail stems become obvious. These leafless, cylindrical, rush-like, light-brown stems appear in April to May. They grow from 10 to 25 cm high and have a rough texture (10). they are jointed, hollow, and tipped with yellowish, club-shaped, spore-bearing heads. Each joint is ridged, grooved, and edged with a short papery sheath notched with 8 to 12 teeth. The joints readily pull apart. These early, fertile stems scatter their spores to the winds and wither and die in a few weeks. The spore-bearing stems are followed by green 10 to 50 cm-long plume-like branches (10) which are produced all summer. These branches, often occurring in great numbers, give the appearance of a horse's tail (10). They are usually four-angled, but sometimes have only three sides; they are jointed but not hollow (13). The green horsetails are the food-assimilating part of the plant, of course, and furnish the rhizomes with nutrients required for the following year's fruiting season.
Horsetail's upper growths are like surfaced periscopes, giving no indication of the industrious bulk of underground parts. They spring from hairy, dark brown branching stems going several feet deep into the ground and bearing dark tubers that are ready to be detached to form new plants (7). Horsetail roots have a great capacity to take up soil nutrients, and many other things as well. A visible amount of gold was recovered from the ash of a large crop of horsetails (7). The plant also can secrete very useful quantities of cobalt and calcium, and of silica, which is a particularly effective fungicide for deterring black spot on roses and mildew on any plant. Horsetail tea can be used to prevent mint rust, and the rust that attacks mallows such as hollyhocks (7). Its mineral talents make horsetail exceedingly valuable in the compost heap. If the compost is not hot, horsetail can be burned and its ashes composted (3). NOMENCLATURE AND HISTORY
Nearly 2000 years ago Pliny, the Roman naturalist, gave field horsetail the name Equisetum arvense (7), which Carolus Linnaeus (1707-1778) adopted in his Species Plantarum in 1753 (1). The botanical name is derived from the Latin equua, a horse, seta, a bristle, and arvens, of the field (9). Occasionally the plant is confused with marestail, an aquatic plant of the genus Hippuris. While it is not related to horsetails, at one time the two plants were commonly believed to be males and females of the same species, the females living in the water, and the males invading gardens from neglected fields (7). Equisetum is the only genus in the Equisetaceae. The genus includes about 25 species (14). Field horsetail is also known by many other names: meadow pine, green foxtail rush, pinetop, pinegrass, snakegrass (5), horsetail fern, bottlebrush, and horse pipes (13).
Horsetail is often known as scouringrush. The fur-rowed stems, structurally reinforced by fine grains of silica, are so hard that they were once used by house-wives for scouring churns and pans, and by cabinet makers as fine, sandpaper-like buffers (7). Gerard (6) reports that horsetail, known as "Dutch rush," was exported from Holland to England and sold in bunches for polishing metal. Some used it to scour pewter, and knew it as "pewterwort." It was also used by comb makers to polish their work. In 1577 the word horsetail for equisetum first appeared in English in Herebach's Husbandry, where B. Goode wrote, "For pasture or meddowe, the woorst as Plinie saith, is russhes, fearne, and horsetayle" (15).
HORSETAILS AS MEDICINE
Dried horsetail is sold in some herb shops for human consumption. Horsetail tea is an ancient remedy that has retained the respect of herbalists for its soothing and curative effect on disordered bladders; it is used for bathing inflammations and reducing swellings; it is also prescribed for clearing up troublesome skin eruptions, and has other uses as well (7). Dioscorides (4) reported that a poultice of the crushed plant helped heal cuts and wounds, and the juice from washed, crushed plants could be taken for stomach hemorrhage. The species most used in medicine was field horse-tail4. Its use dates at least to the time of the Romans, who applied the bruised leaves to bleedings and added the young shoots to salads for their tonic effects. The poorer people even ate the green parts as a rather unpalatable vegetable dish. During the medieval period it was regarded as a valuable wound herb. According to Culpeper (2), it was "very powerful to stay bleedings, either inward or outward." It would also "cure ruptures in children, heal running ulcers and excoriation of the Applied outwardly in a warm compress, horsetail reputedly eased "inflammations and other eruptions of the skin" and "the swelling heat and inflammation of the fundament or privy parts, in men and women" (2). The sterile stems of field horsetail are still used for their diuretic and astringent principles, mainly in liquid or fluid extracts, decoctions, or teas. The herbal-minded may take horsetail for dropsy and kidney complaints, ulcers of the urinary tract, hemorrhages, and for soothing disordered bladders. Decoctions applied as a wash will help stop wounds from bleeding and ease inflammations, swelling, and various skin eruptions (3).
HORSETAILS AS POISONOUS PLANTS
Probably every species of Equisetum is poisonous to certain animals. Since the late 1800s, cases of Equisetum toxicity to livestock have been reported in the U.S. and Canada. According to Kingsbury (10), there is a relationship between species of Equisetum and class of livestock poisoned. The largest number of instances involves poisoning of horses who consumed E. arvense in hay. Hay composed of one-fifth or more E. arvense produces symptoms in horses in 2 to 5 wk (8). Unthriftiness is followed by weakness; the animal's appetite remains normal almost to the end. In fatal cases death is preceded by quiescence and coma. Removing contaminated hay in the early stages of poisoning brings about rapid recovery (8).
In North America, field horsetail is the sole documented culprit in Equisetum poisoning of horses, although cases in sheep have been mentioned (10). Georgia (5) reports affected sheep become thin and lack good condition but do not die. The second most frequently recorded poisoning in the world literature is that of cattle by E. palustre. It and field horsetail have proven toxic to additional classes of livestock in Europe (10). However, E. arvense is rarely, if ever, lethal to cattle (8). Researchers have suggested various factors as the toxic principle in Equisetum species, viz: silica, aconitic acid, palmitic acid, nicotine, equisitine, palustrine, and dimethylsulfone (10). Now none of these is currently believed the source of toxicity.
The deep-seated system of roots and rhizomes with tuberous storage organs make horsetail very difficult to eradicate. A combination of improved drainage, clean cultivation, and application of fertilizer to stimulate crop plants will gradually eliminate horsetail (13).
1. Britton, N. L. and A. Brown. 1898. An Illustrated Flora of the Northern United States, Canada and the British Possessions. Volume I. Charles Scribner's Sons, New York.
2. Culpeper, N. 1802? Culpeper's Herbal or The Complete English Family Physician, with additions by G. A. Gordon. Hogg and Co., London.
3. De Bray, L. 1978. The Wild Garden. Mayflower Books, Inc., New York.
4. Dioscorides, P. 1959. The Greek Herbal of Dioscorides. R. T. Gunther, ed. Hafner Publ. Co., New York.
5. Georgia, A. E. 1942. A Manual of Weeds. The Macmillan Co., New York.
6. Gerard, J. 1928. Gerard's Herbal. Houghton Mifflin Co., Boston.
7. Hatfield, A. W. 1969. How to Enjoy Your Weeds. Frederick Muller, London.
8. Henderson, H. V., E. V. Evans, and R. A. McIntosh. 1952. The antithiamine action of Equisetum. J. Am. Vet. Med. Assoc. 120:375.
9. Jaeger, E. C. 1944. A Source-book of Biological Names and Terms (2nd Ed.). Charles C. Thomas, Springfield, IL.
10. Kingsbury, J. M. 1964. Poisonous Plants of the United States and Canada. Prentice-Hall, Inc., Englewood Cliffs, NJ.
11. LeStrange, R. 1977. A History of Herbal Plants. Angus & Robertson, London.
12. Mitich, L. W. 1981. The intriguing world of weeds, Part X. Weeds Today. 12:15.
13. Muenscher, W. C. 1948. Weeds. The Macmillan Co., New York.
14. Robbins, W. W., M. K. Bellue, and W. S. Ball. 1951. Weeds of California. Calif. Dep. Food & Agric., Sacramento.
15. Simpson, J. A. and E.S.C. Weiner. 1989. The Oxford English Dictionary, 2nd Ed. Clarendon Press, Oxford.