Ferns are among the oldest types of plants still surviving on the planet, and some species have remained virtually unchanged for tens of millions of years. They are also one of the most diverse groups of plants, with thousands of species spread across most temperate parts of the globe.
During the Carboniferous Period, which ended about 300 million years ago, ferns were the dominant form of plant life on Earth, and although many ancient ferns were nearly identical to fern species alive today, the Carboniferous forests were home to towering tree ferns that created a canopy under which smaller ferns grew.
Although modern tree ferns, which are much like their ancient ancestors, have structures similar to other ferns, they grow to immense sizes and resemble full-size tropical trees. The Australian tree fern (Sphaeropteris cooperi) grows in U.S. Department of Agriculture plant hardiness zones 10b through 11, and it can be grown indoors in a container. This fern grows a single trunk that can be up to 12 inches in diameter, and it unfurls fronds that are between 12 and 18 inches long. This tree fern can grow 15 to 30 feet tall.
Many fern species grow in the shady, moist environments under forest canopies and blend into the undergrowth, but not all ferns are green. Some species are nearly as showy as vibrant garden flowers. The new growth of some ferns is strikingly orange, red or yellow, and some species have brilliantly colored stems or variegated leaves.
The Japanese painted fern (Athyrium niponicum var. "Pictum") is a delicate, low-growing fern that grows in USDA zones 5 through 8. Its red-purple leaf stems contrast with the silvery sheen of its leaflets, and it grows in 8- to 12-inch-tall clumps that hug the soil.
Fern leaves are called fronds, and their structure is different than other plants. Fern fronds usually sprout directly from the plant's underground structure without any stem, and the fronds gradually unroll from base to tip, forming the familiar "fiddlehead" shape in the process.
Fern fronds are made up of a central stem called a rachis and small leaflets that grow along the rachis. In some species, the frond is divided, with a smaller rachis branching from the central stem; then an even smaller rachis branches from that one, until the frond is divided as many as four or five times.
Spores, Not Seeds
Most flowering plants reproduce through seeds that develop from flowers, but ferns have neither flowers nor seeds. It's their lack of seeds that sets them apart from both flowering plants and cone-bearing plants.
The fern's life cycle begins when the adult fern plant, called a sporophyte, produces and sheds spores, tiny seedlike capsules that are dispersed by water or wind to a location away from the parent plant. In the new spot, the spore germinates and produces a new plant, called a gametophyte. The gametophyte, which is often tiny and inconspicuous compared to the sporophyte, then produces both egg and sperm cells. The sperm cells fertilize the egg cells, and the fertilized egg grows into a new sporophyte.