The botony of ferns
Ferns, which are among the oldest plants on earth, are very different in their structure and their reproduction from flowering plants. Instead of stems, ferns have stipes. Instead of leaves, ferns have pinnae. Instead of seeds, ferns have spores.
The whole leaf of the fern is the frond, composed of the stipe (stem) and the blade or expanded leafy part of the frond. The stem within the blade is called the rachis, while the lower stem is the stipe. The leaf consists of pinnae and the divisions of the pinnae are pinnules. These can be divided also into smaller parts. Pinnae can be once-cut like Christmas ferns, twice-cut like ostrich ferns or thrice-cut like lady ferns, which are very lacy.
Underground is the rhizome with hairlike roots. The crozier-like leaf bud that arises from the rhizome in the spring is the fiddlehead. Ostrich fern fiddleheads are edible and prized by gourmets.
Spores are the main form of reproduction. The spores of most ferns are found on the underside of the pinnae. Marginal fern spores range along the edge or margins of the fern, hence the name. Maidenhair ferns produce an indusium or fold along the edge which protects the spore cases. Spore cases of lady fern look like commas or half moons while most spore cases are round. Some ferns, like the sensitive fern and the royal fern, produce separate spore stalks. Each fern can produce millions of spores.
Spores which land on fertile ground and germinate, like seeds, produce a unique stage in the fern’s life: the prothallus, a tiny plant the size of a thumbnail. Both male and female organs emerge and sperm reaches the eggs through the medium of water in the form of rain. The young recognizable fern emerges from the fertilized egg.
— CHERYL B. WILSON