Ferns are all leaf, all the time—no slow preparation for the momentous flower, no seduction of the insect. At the tips of young fronds, fiddleheads unfurl, fronds lengthen, leaflets appear and widen behind the unfurling tip like the widening wake behind a boat. My store-bought Boston fern, tended for years with no expertise, bears dazzling fronds that arch up, out, and over—a fountain of green.
Ferns were among the earliest plants with roots to dig deep for water and vascular stalks and stems to transport it throughout the plant. They were the first to grow arrays of hundreds of leaves. This was almost 400 million years ago. Earlier plants had lived entirely in the water, with no need for deep roots. On land, before the ferns, the first mossy plants, lacking roots or stems, could grow no higher than a few inches. Vascular tissue—tubes that conduct fluids, minerals, and gasses—changed everything. Ferns reached the height of trees. And today vascular systems circulate the red blood through us all.
Ferns emerged late in the Devonian Period, which lasted from 419 to 359 million years ago. About 30 million years prior to the Devonian, the first of Earth’s five mass extinctions took place. The climate cooled, water froze, glaciers grew, the sea level fell, coastal and ocean habitats disappeared. As the earth warmed again, carpets of moss sprang up along lakes and streams and bony, heavy-jawed fish swam in the seas. Then ferns and other plants became the first forests.
Toward the end of the Devonian, the second mass extinction took place. It came in three pulses. Ocean species, including the heavy-jawed fish, disappeared. But land plants, including the ferns, were mostly spared. In fact, one theory (bbc.com/earth/story) holds that the roots of the ferns and other plants broke through rocks and released nutrients into the lakes, rivers, and oceans. The nutrients fed huge blooms of algae which later died and decayed, taking up the oxygen that had kept the fish alive. Meanwhile, again, the ferns thrived.
Ferns proliferated in part because of how they propagated. Here they were—and are—old fashioned. Instead of reproducing via miniaturized plants embodied in seeds, ferns spread through spores, single cells released from the underside of the fronds. When the spores settle on moist soil, they grow a tiny intermediate plant that will provide the fertile start for the new fern. Spore propagation seems a complicated two-step process, but the lightness of the single-celled spores let them disperse on the wind and germinate on distant, moist soil.
Some days I gawk at a plant whose distinctive family features date back 400 million years. No other plant or animal that I see every day goes back almost to the start of life on land. The ancestors invented leaves and roots but kept the old method of reproducing. They survived four mass extinctions, as well as the flowering plants that burst on the planet 125 million years ago and dominated the plant kingdom. Ferns watched the dinosaurs come and go. Today they regale us with tales of ancient climates and their durable adaptations.
Note: Among the sources on ferns, Don Lubin’s “Introduction to Ferns” is especially readable and informative for the general reader.