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Subclass Polypodiidae
Subclass Polypodiidae
The true ferns or leptosporangiate ferns consist of over 12,000 species of spore-bearing, vascular plants that have complex vasculatures (siphonostele), and frequently compound leaves, called fronds. Almost all ferns have circinnate vernation, which means that they create new leaves as fiddleheads that uncurl during maturation. Sporangia are produced on the lower (abaxial) surface of leaves in clusters called sori. They are the most successful (living) spore-bearing plant group, showing a diverse range of habits and forms: herbaceous forms, floating forms, tree-like habit, even vines.
Above: (left) cross-section through a fern rhizome showing the siphonostele; (left-middle) sori on the bottom side of a fern frond; (center) new fern fronds called fiddleheads or croziers emerging in spring; (right-middle) fertile fronds of a regal fern, Osmunda regalis; (right) compound leaf of Pteridium
Diversity
Diversity
Represented by 7 extant orders, 44 families, ~250 genera, and ~12,000 species
Classification
Classification
└Tracheophytes
└Euphyllophytes
└Ferns (Polypodiopsida)
└Polypodiidae
Geologic Range
Geologic Range
Early Carboniferous - present (Galtier & Scott, 1985; Galtier & Phillips, 1996);
By the end of the Carboniferous, six families were present.
In subsequent major filicalean radiations in the Permian, Triassic, and Jurassic, several families (e.g., Osmundaceae, Schizaeaceae, Matoniaceae, and Dipteridaceae) with extant representatives replaced these Carboniferous families (Rothwell, 1987).
Sporophyte (spore-bearing phase)
Sporophyte (spore-bearing phase)
Vegetative features
Vegetative features
Stems
Stems
Usually underground rhizomes, although upright stems are found in tree ferns
Water ferns have highly modified stems
Leaves
Leaves
Most true ferns have large compound leaves, called fronds
Leaves can be once to several times pinnate
Some palmately compound and simple leaf (e.g., Asplenium) species exist
New leaves form as fiddle heads or croziers
This is called circinate vernation ("vernation" is the pattern of leaf growing or unfolding in plants)
Reproductive features
Reproductive features
Sporangia grow on underside (=abaxial) surface of leaf
Sporangia are clustered into a sorus (plural = sori)
Each sporangium has a thickened "mohawk" structure to disperse spores, called an annulus
True ferns are leptosporangiate: tiny sporangia, with 12-128 spores, and an annulus, which develops from a single initial cell
Gametophyte (gamete-bearing phase)
Gametophyte (gamete-bearing phase)
Gametophytes are small, but multicellular and free-living
Most ferns have photosynthetic gametophytes
Monoecious and dioecious forms exist
Above: Large fiddleheads of a tree fern in the NYBG Conservatory
Above: Gametophyte of a fern
Below: Gametophyte with an emerging sporophyte
Additional Reading
Additional Reading
Desiccation tolerance of terrestrial fern gametophytes is linked to light levels in the sporophyte habitat in a cloud forest (Pinzón-Camacho et al., 2025)
Fern stems reveal secrets of evolution – how constraints in development can lead to new forms (The Conversation, 25Nov2025)
└Fern vascular architecture reveals how developmental constraint can generate novel morphology (Suissa, 2025)
A fern that makes rare earth elements (Phys.org 13Nov2025)
└Discovery and Implications of a Nanoscale Rare Earth Mineral in a Hyperaccumulator Plant (He et al., 2025)
Fern leaf pockets hide secrets of plant-microbe symbiosis (Phys.org 18Aug2025)
└Armitage et al. (2025) Adaptive pangenomic remodeling in the Azolla cyanobiont amid a transient microbiome
Cracking the Case of the Giant Fern Genome (12Sep2022, NY Times)
Fossilized nuclei reveal Jurassic genome in ferns (Paleoplant Blog 12Dec2014)
YouTube tutorial about fern lifecycle (YouTube 27Oct2010)
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