Classified as non-flowering plants, ferns evoke images of cool woodland shade, misty vistas and feathery foliage. As with palms and cycads, the leaf of a fern is called a frond. As the frond first emerges, it unrolls as it lengthens, leading to the name of fiddleheads. Young, unrolling fern fronds are also called croziers.
The fern frond comprises two parts: the stipe and the blade. The stipe is the leaf stem, leaf stalk or stem petiole. The blade makes up the balance of the frond. The stipe becomes the rachis in the part of the frond where the blade grows. The blade structure and appearance varies according to species; some are undivided and entire while other are deeply and finely cut. The term pinnate plays a central role in describing the fern frond. When small leaflets in the fern blade display into two branching ranks, the fern is called bipinnate. Other, more intricately branching blades may attain the descriptors tripinnate and so on, depending on the number of times smaller rank branching develops. When fern leaf segments grow immediately alongside the rachis, it is described as being pinnatifid.
Fern fronds carry two functions: food production and reproduction. Fronds that do not develop reproductive spores on their undersides are considered sterile. The sterile fronds' function is gathering of light for photosynthesis and creation of carbohydrates for the plant. Fronds that do develop the tiny green, brown or black dots on their undersides, or spore bodies called sori, are called fertile fronds. Even though their most important function centers around spore production, they also contribute to making food since they are leaves conducting photosynthesis.
With over 12,000 species of fern species, the size of fronds is limited only by physics and plant physiology. Tree ferns, such as those in the botanical genus Cyathea or Dicksonia, develop fronds as long as 12 feet. Conversely, the aquatic floating mosquito fern's (Azolla spp.) fronds grow no larger than 1/16 to one inch.
Depending on fern species and climate, fern fronds persist only during the frost-free growing season or remain evergreen. Ferns with deciduous foliage often grow naturally where a seasonal dormancy in winter or drought allows the plant to survive many years. Evergreen ferns keep their foliage and turn different colors, even in cold winters, but these will die and need to be replaced after two to ten growing seasons.
For humans, fern fronds serve as foodstuffs for domesticated animals as well as decorative shade-casting leaves, as in the case of large tree ferns. The beauty of the foliage colors and textures means that ferns are often grown in gardens, as house plants and also cut to embellish floral arrangements.