400 Million Years of Ferns

Ferns are all leaf, all the time—no fanfare for a celebrated flower, no seduction of the insect. At the tips of slender sprouts, curled fiddleheads unfurl while leaflets widen behind the unrolling tip, like a wake spreading behind a boat. My store-bought Boston fern, tended for years with no expertise, is a fountain of green, bearing dazzling fans of leaves that arch up, out, and over.

Before ferns, all plants lived entirely in the water, where they did not need roots or stems. But about 450 million years ago, Earth endured the first of its five mass extinctions to date. The climate cooled, water froze, glaciers grew, the sea level fell, coastal and ocean habitats disappeared. But new land was exposed, and when the climate warmed again, plants grew there.

The first of these land plants were mosses. Carpets of moss sprang up along lakes and streams. But without deep roots or firm stems, mosses grew no higher than a few inches. Thriving on land requires tubes that can carry liquids up and throughout an organism. Ferns were among the earliest plants with roots to dig deep for water and stalks and stems to transport it throughout the plant. Vascular tissue changed everything. Ferns reached the height of trees.

Devonian ferns wikimedia

wikimedia

And ferns became expert at growing efficient leaves. They needed to do so to capture carbon dioxide whose levels fluctuated over the millennia. Declines in the atmosphere’s carbon dioxide led to cooling temperatures. But the hundreds of leaves on even a small fern were ready to soak up enough carbon dioxide to keep the fern going. Today, healthy ferns withstand cold weather better than most plants.

Ferns have multiplied the world over in part because of how they propagate. In this respect, they were and are old fashioned. Instead of reproducing through 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 create the male and female components for the start for a new fern. Spore propagation seems a complicated two-step process, but the lightness of the single-celled spores lets them disperse on the wind and germinate on distant, moist soil.

Some days I gawk at a plant whose distinctive features date back nearly 400 million years. No other plant or animal that I see every day goes back almost to the start of life on land. A fern’s 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 came to dominate the plant kingdom. Ferns watched the dinosaurs come and go. Today they regale us with tales of ancient climates and their ingenious survival skills.

 

 

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