Horsetail (Equisetum spp)

Main sources: Florida International website;

UCMP Taxon Lift: Sphenopsida

Horsetail is a member of the ancient Sphenopsid clade, which is a sister to the Ferns, both groups first appearing during the Carboniferous Period (350-290 mya) of the Paleozoic Era. Unlike most of the early land plants (except for the Lycopodia, ancestors of todays "Club Mosses"), both these clades have living representatives, though today's variety and prominence is much reduced from Paleozoic times. Horsetail shows the typical Sphenopsid features: node/node morphology (joint-to-joint construction of stems), whorled arrangement of parts, reduced leaves, ridged and grooved stems, "hollow" stems with a large, empty pith cavity, terminal cones containing spores, and clonal rhizomes. Fossil Sphenopsids called Calamites reached 30 feet in height during the Carboniferous Period, and were prolific, judging by their fossil presence in the coalbeds dated to that time.

Today, Horsetails reach only 2 to 5 feet high. They are consistently found in riparian locations where their rhizomes are in contact with saturated soil, and can produce colonies of aerial stems. We see the plant in our Saguaro Juniper area particularly in Hot Springs Canyon where the stream is perennial, above the Zig Zag bend (and it may be spreading downstream along with recovery of other riparian plants above the Yellow Cliffs).

Horsetail produces silica in its epidermis, by virtue of which some varieties are called "Scouring Rush" (the plant being used as a cleansing abrasive.) Medicinally, it has been widely used around the world since ancient times for a wide variety of ailments (just search the Web under "Horsetail" for an endless variety of contemporary examples).

It can be very toxic to horses. For a detailed diagram and description of plant characteristics, see this link: Purdue U. School of Veterinary Medicine Website.

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