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Figure 21.13 Horsetail spores. A. With elaters coiled. B. With elaters spread.

Hopi Indians ground dried horsetail stems to flour, which they mixed with cornmeal to make bread or mush. Horsetails have, however, occasionally been reported to be poisonous to horses, and they are not recommended for human consumption.

Native Americans and Asians had several other uses for these plants. One tribe drank the water from the carinal canals of the stem, and another thought the shoots were "good for the blood." It is not known if there was any basis for this latter idea, but there is an old unconfirmed report that field horsetail consumption "produces a decided increase in blood corpuscles." At least one or two species are known to have a mild diuretic effect (a diuretic is a substance that increases the flow of urine), and they have been used in the past in folk medicinal treatment of urinary and bladder disorders. Some have also been used as an antacid or an astringent (an astringent is a substance that arrests discharges, particularly of blood). One species was used in the treatment of gonorrhea, and others were used for tuberculosis.

At least two Native American tribes burned the stems and used the ashes to alleviate sore mouths or applied the ashes to severe burns. Members of another tribe ate the stro-bili of a widespread scouring rush to cure diarrhea, and still others boiled stems in water to make a hair wash for the control of lice, fleas, and mites.

During pioneer times when the covered wagons moved westward, the use of scouring rush stems for scouring and sharpening was widespread. They were used not only for

Carboniferous Reconstruction
Figure 21.14 Reconstruction of a coal age (Carboniferous) forest. (Photo by Field Museum of Natural History, Chicago)

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Figure 21.15 Reconstruction of the fossil giant horsetail, Calamites.

cleaning pots and pans but also for polishing brass, hardwood furniture and flooring, and for honing mussel shells to a fine edge. Scouring rushes are still in limited use for these purposes today. Some species of horsetails accumulate certain minerals in addition to silica. Veins of such minerals have been located beneath populations of horsetails by analyzing the plants' mineral contents. This process of analysis involves a chemical treatment of the tissues followed by the use of X-ray equipment.

In the geological past, the giant horsetails and club mosses were a significant part of the vegetation growing in vast swampy areas. In some instances, the swamps were stagnant and slowly sinking, permitting the gradual accumulation of plant remains, which, because of the lack of oxygen in the water, were not readily attacked by decay bacteria. Such circumstances, over aeons of time, were ideal for the formation of coal. Today, if you section a lump of coal thinly enough and examine it under the microscope, you can still see bits of tissue and spores of plants that were living hundreds of millions of years ago. One soft coal known as cannel consists primarily of the spores of giant horsetails and club mosses that, through the ages, were reduced to carbon.

For the scientific names of species discussed, see Appendix 1.

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