Plant Relics are Humble but Handy

Plant Relics are Humble but Handy

Meadow horsetail. Image by Elinor Osborn.

Three hundred million years ago, dinosaurs roamed the land. The earth they inhabited was hot and humid and covered in vast, swampy forests that today would seem most bizarre.

Some of the plants growing then resembled giant bottle brushes, reaching 60 feet tall. Others sported 100-foot-tall trunks that were clothed in overlapping, scalelike leaves. Notably absent were flowers: it would be another 200 million years before flowering plants evolved.

Although the dinosaurs are long departed, victims of a bygone natural catastrophe, some of the plants in their landscape stubbornly survived. Their relatives exist today in more modest forms.

Horsetail is one such “prehistoric” plant. About 10 species of horsetails grow in the Northeast; they are often found in wet soils and semiaquatic areas but can be found in sites that are quite dry. The plant has hollow, jointed stems, and some species have threadlike side-branches that are commonly mistaken for leaves. But the leaves of these horsetails are tiny, so they rely on green side branches and a green main stem for photosynthesis.

Horsetails appear almost unchanged from the earliest plants that made the transition from water to land some 400 million years ago. Lacking flowers, a horsetail reproduces by spores from a cone that grows at the tip of its stem. Each spore bears long, ribbonlike extensions that allow it to be dispersed by air currents. If it lands in a damp place, a spore grows into an entirely different and independent plant. This tiny plant, known as a prothallus, can be either male or female. Male prothalli produce sperm that, when washed off the plant by rain, float to find and fertilize the eggs in nearby female prothalli. Once fertilized, eggs develop into the sporeproducing horsetail plants that we commonly see. This two-stage life cycle is called the “alteration of generations.”

As horsetails evolved, they developed a means to stand upright without the support of water. Their hollow stems became reinforced with the mineral silica. Horsetails are scratchy due to this high silica content, and centuries ago, we humans began using them as an abrasive to scour pots and put fine, smooth finishes on pewter and silverware. Nowadays, horsetail silica, finer than any silica powder devised by humans, is used to polish certain medical and dental products.

Another age-old plant is clubmoss. While horsetails can flourish in various locations, clubmosses are more restricted, growing mostly in the cool, shaded environment of the boreal forest. Clubmosses are low plants with creeping, branched stems that hug the ground. Since they resemble miniature evergreen trees, they are commonly known as ground cedar, ground pine, or princess pine. When these plants were in their heyday 300 million years ago, during the Carboniferous Period, an estimated 50 percent of the world’s vegetation consisted of giant clubmosses. Today their fossil remains make up coal deposits with enormous economic value.

Today’s clubmosses, tiny in comparison to their towering ancestors, have modernday economic value. In some areas, some species are harvested in huge amounts to make Christmas wreaths. Because it can take up to 20 years for clubmosses to complete their reproductive cycle, it’s important to harvest this plant in a sustainable way. Clip mature stems near ground level rather than ripping or tearing them up (this protects rhizomes). Harvest no more than 25 percent of a plant’s “greens” in a season, and then give the area a few years to regenerate before you return.

Like horsetails, the clubmosses we see reproduce via spores rather than by flowers and seeds. The spores are shed from the club-shaped, yellowish cones that arise from their tips or from spore-bearing structures in the axils of the leaves. Although each spore is microscopic, being only one-fortieth of a millimeter across, masses of them are collected for various uses. The spores, also known as “vegetable sulfur,” have high oil content, which makes them extremely flammable when airborne. Early photographers ignited the spores for flash photography, and the spores are still sold today for magic tricks and other theatrical special effects. Clubmoss spores also are used as tracers in certain types of scientific research and as an ingredient in some medicines and cosmetics.

Although horsetails and clubmosses are considered evolutionary relics, they are easy to spot in the Northern Forest. And unlike many inorganic relics, these humble plants have modern-day utility.

 
Discussion
  1. Walter E. (Ted) Auch β†’ in Burlington
    Aug 24, 2010

    While I loved the piece, I was struck by the comment that clubmosses are mostly found β€œin the cool, shaded environment of the boreal forest.” This is factually incorrect. I have hiked the White, Green, and Adirondack ranges frequently and have actually never seen Lycopodium - my favorite understory plant - beneath boreal forests if I am to assume the definition of boreal is spruce-fir either entirely or intermittently. Rather you are more apt to find this beautiful relic beneath mesic to dry beech, beech-maple, and beech-birch-maple in the aforementioned mountain ranges. This is an important distinction and one your readership should understand if they don’t already. Lycopodium is truly a jewel of New England’s hardwood forests, not its boreal forests.

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