Ferns are an ancient group of plants that date back about 300 million years. They have a remarkable way of reproducing from microscopic spores rather than seeds. The bumps that you see on the undersides of the fronds are spore cases, called sporangia. The spores inside the spore cases are the beginnings of a fascinating life cycle.
Life Cycle of a Fern
When the spores are mature, the spore case ruptures and releases them to the wind. If they land in a favorable environment, they germinate and develop into a flat, heart-shaped, leaf-like structure called a prothallium. Sexual organs develop on the underside of a prothallium, producing sperm and eggs. Moisture on the prothallium allows the sperm to swim to the egg, and fertilization occurs. It takes two to six months for a fertilized egg to produce a frond.
Ferns can be divided into two groups: hardy and tropical. Hardy ferns, such as Christmas ferns (Polystichum acrostichoides) and sensitive ferns (Onoclea sensibilis) tolerate winter temperatures in U.S. Department of Agriculture plant hardiness zones 3 through 8, but don't like extreme heat. Tropical ferns such as the Boston fern (Nephrolepis exaltata), which is hardy in zones 9 through 11, are grown outdoors in mild climates or kept as houseplants.
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