Nebraskaland

June 2021 • Nebraskaland 57 Where are the Seeds? Like other ancient plants, ferns reproduce through microscopic spores. Early botanists, who had no knowledge of spores, were baffl ed as to how ferns reproduced. "Where are the seeds?" they pondered. In medieval Europe, herbalists concluded the seeds must be invisible. Better yet, they bestowed invisibility upon those who possessed them, a god-send for the superstitious, and perhaps not-so-wise thieves and other doers of mischief. Finding the seed usually involved magic and roaming the woods at midnight, sometimes barefooted. If one failed in this adventure, it was often because fairies, goblins or demons had, at the last second, snatched the seed from the seeker's grasp. In the late 1700s and early 1800s, botanists, using the newly-invented microscope, unwrapped this fern mystery, fi nding "they had no seeds" and that their young arose from the "fern dust" that fell from the bumps on the underside of their leaves. Decades later, the dust was discovered to be spores, and the fern life cycle was fi nally understood. To this day, the complicated life cycle, quite diff erent from that of fl owering plants, still confounds botany students and leaves them asking, "Why didn't I major in psychology?" Wind-blown Spores Extremely light, fern spores can be blown great distances by wind. They have been found high in the atmosphere where they survive extreme cold and intense ultraviolet radiation. At such altitudes, air currents could carry spores hundreds, if not thousands, of miles. Recently, three colonies of the never- before-seen-in-our-state cutleaf grape fern have been discovered: two in the woods at Indian Cave Park and one 40 miles to the north near Nebraska City. For more than a century, could botanists have overlooked this plant in Nebraska, or are the colonies of recent origin, their spores wind-blown from populations in northeastern Kansas? In recent decades, the ebony spleenwort also appears to have migrated into southeastern Nebraska, also likely from Kansas populations. If these are spore-instigated migrations, why are they occurring now? Could it be due to climate change? Perplexing Distributions Sensitive fern and marsh fern, both found in wetlands in the Sandhills and spring seeps in eastern Nebraska, and several other mostly woodland ferns have perplexing distributions. They grow in eastern North America and eastern Asia and nowhere else. Why? The answer to this mystery lies deep in geological time. During the early Tertiary Period, 54 to 38 million years ago, the Earth's climate was much warmer than today, allowing deciduous forests to span the globe at high, northern latitudes. In North America these forests extended into Alaska and Greenland and crossed land bridges westward into Asia and eastward into Europe. The above- mentioned ferns spread throughout The Fern Life Cycle The single-celled fern spores develop in elongate to round, brownish bumps on the underside of the plant's leaves known as sori. When ripe and the air is dry, an ingenious lever-like action, which responds to humidity, catapults the spores skyward to be carried by the wind. If, by chance, a spore lands on moist soil or other suitable surface, it germinates and grows into a flat, green, heart-shaped structure that bookish botanists call a prothallus. Less than a quarter-inch in size, prothalli are usually hidden by other vegetation and are noticed by only the most inquisitive. The prothallus under-surface bears sex cells that produce either egg or sperm. During rains, or whenever water is present, the sperm are released and, using their whip-like tails, swim to the egg. Once fertilized, the egg grows into the well-recognized fern life stage with roots, stem and leaves.

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