Botany, Seasons

Evergreen and Everlasting: The Long March of the Lycophytes

Artist’s rendering of a Carboniferous swamp. From “The World Before the Deluge” by Eduard Riou, 1872. Public domain work of art.
Artist’s rendering of a Carboniferous swamp. From “The World Before the Deluge” by Eduard Riou, 1872. Public domain work of art.

By Julia Runcie –

In the murky, humid forests of the Carboniferous Period, organisms grew to remarkable size. Dragonflies as big as Cooper’s hawks ruled the air and three-foot-long scorpions prowled the earth. The swampy water concealed beasts like the dawn tadpole, a predatory amphibian as long as a pickup truck. The canopy showcased elegant tree precursors: spore-bearing lycophytes a hundred feet tall.

Today, dragonflies are rarely any bigger than a clothespin. Tadpoles are tiny and harmless, and scorpions could fit in your palm (not that you’d want them there). This widespread diminution may be related to a dramatic decrease in atmospheric oxygen concentration since the Carboniferous. Even the lycophytes have had to shrink to survive. Yet three hundred million years after their age of supremacy, lycophytes persist in forests from the poles to the tropics. We call them clubmosses. They are usually less than four inches tall.

In early November, clubmosses leap into view on the forest floor, bright green runners in a matrix of brown. These evergreen plants are not actually mosses, but true vascular plants more similar to ferns and horsetails. At first glance they are easily mistaken for conifer seedlings; hence the common names ground pine and ground cedar. Lateral stems called rhizomes carry them across the ground. Periodically they send up vertical shoots, which emerge out of the leaf litter to capture sunlight. Having evolved before the seed, clubmosses disperse by means of spores, which most species carry in tiny kidney-shaped pouches packed together on a club-like appendage called a strobilus.

Ground pine (Lycopodium obscurum) with strobilus.
Ground pine (Lycopodium obscurum) with strobilus.

Wind-borne clubmoss spores are easily dispersed, but they have a long road and two life phases ahead of them. After germination, spores develop into tiny, often subterranean organisms called gametophytes. The gametophyte phase is responsible for the production of sex cells, which join at fertilization to form embryos. The embryos develop into the second life phase: sporophytes, charged with the production of new spores. This is the more familiar life phase we see above ground. Note, however, that not every clubmoss has a club: years may pass before sporophytes are capable of manufacturing new spores. Development from the gametophyte to the mature, strobilus-endowed sporophyte can take between six and fifteen years.

Clubmoss spores ripen in the fall, when a light tap to the strobilus is enough to release them. If you stroll through a miniature forest of lycophytes at this time of year your feet will stir up a cloud of gold. This fine powder has been put to use in a litany of applications: as a wood-filler in violins and guitars, a lubricant on condoms and surgical gloves, a hydrophobic coating for pills, and a homeopathic remedy for intestinal disorders. Crime scene investigators once used the spores to dust for fingerprints. The powder is highly flammable; early flash photography relied on the ignition of clubmoss spores. We have incorporated the spores into fireworks and magic tricks, theatrical productions and military operations. For more routine combustion, we turn back to the clubmoss’s progenitors: the giant lycophytes that ruled the swamps of the Carboniferous are burned today as coal.

Ground cedar (Diphasiastrum digitatum) with branched strobili.
Ground cedar (Diphasiastrum digitatum) with branched strobili.

Vermont’s woods can seem a little dull this time of year. Perhaps it will enliven your walk if you pause to remember that you are in the presence of prehistory. The tiny clubmosses at your feet have thrived on earth for hundreds of millions of years. With every step you are releasing spores that could have sealed a violin or cured a stomachache or solved a crime. Instead, because of you, they’ll go on to form a new generation of this enduring lineage.

Information gathered from Cathy Paris, Bernd Heinrich’s The Trees in My Forest, Mary Holland’s Naturally Curious, Encyclopaedia Britannica (retrieved from http://www.britannica.com/science), and Biology of Plants by Peter H. Raven, Ray F. Evert, and Susan E. Eichhorn.

Julia Runcie is a first-year student in the Ecological Planning program.

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