In prehistoric times, when we had a warm, moist, and stable climate, Ferns were some of the most plentiful plants to be found. Many of those growing at that time are now extinct, but as the climate cooled, many ferns adapted to the forms we see today, numbering over 12,000 worldwide including 400 in the U.S. and about 100 in the northeastern U.S. Ferns were among the first plants with vascular systems containing an internal system of tubes allowing for water and nutrient movement throughout the plant and providing support for an upright stance. There were no flowers, and their reproductive process, using spores, was not discovered until the late 1600s and not well understood until the mid-1800s.
Leaves, called fronds, have specialized cells on the bottom side called sporangia that produce spores. Sporangia first appear as small white or green dots, but as spores mature over time, they turn shiny and dark brown. Several hundred thousand to several million spores are created by each fern. When they are mature, spores are ejected by a variety of methods from being shot into the air to simply floating away on a slight breeze. If they do not land in a favorable environment, they can remain viable for up to a year.
The reproductive process, called alternation of generations, has both sexual and asexual components. In the asexual process, spores grow by dividing and forming a small structure called a prothallium that gets its water and nutrients directly from the soil. The prothallium divides into two more structures, the archegonium, containing an egg, and the antheridium, containing sperm. In the sexual process, sperm swim to the eggs, fertilize them, and a new plant begins to grow. The young fern, also known as a fiddlehead, is a tightly coiled collection of new fronds that pokes through the soil surface in spring. As growth continues, the flat, green fronds uncurl and have many leaflets on either side of a midrib stalk. Photosynthesis takes place in the fronds, producing food for the plant.
Spores represent the normal process for reproduction in most ferns, but some can reproduce strictly asexually by cloning of fronds, roots, or rhizomes. The walking fern, Asplenium rhizophyllum, a rare species found in dolomite canyons around Lake Michigan, are an example of cloning as they tip their fronds over till they touch the ground and start a new plant.
Ferns come in a variety of sizes, from two inches to eight feet tall. They grow in most habitats, although they are rare in deserts. There are several ferns growing in the DuPage area that you may enjoy finding and learning about. The Christmas fern, Polystichum acrostichoides, is an evergreen plant growing in rich, moist wetlands and forests. Adder’s tongue fern, Ophioglossum pusillum, is found in fens and marshes, particularly areas with sandy or gravelly soil. Interrupted fern, Osmunder claytoniana, which got its name from the Saxon god, Osmunder the Waterman, who hid his family under the fern while fleeing his enemies, can be found on woodland slopes where there is seepage. Look for these as well as other species to enhance your hiking experiences.
