Site focus
   Navigating the site
   Why ferns are hard to identify
   Illustrated Glossary
   Flora of Australia
   Lower Vascular Plant Glossary
Hardy Fern Glossary
   Structure and Shape
   Blade Division
   Hairs and Scales
   Sori and Indusia
Major Fern Links

    Adiantum  Arachniodes
    Aspidotis  Asplenium
    Astrolepis  Athyrium
    Blechnum  Cheilanthes
    Cryptogramma  Cyrtomium
    Cystopteris  Dennstaedtia
    Deparia  Diplazium
    Dryopteris  Gymnocarpium
    Lygodium  Matteuccia
    Onoclea  Oreopteris
    Osmunda  Pellaea
    Phegopteris  Pleopeltis
    Polypodium  Polystichum
    Pteridium  Pteris
    Pyrrosia  Thelypteris
    Woodsia  Woodwardia


The most remarkable aspect of pteridophyte nomenclature is how unsettled it is. There is little agreement about what constitutes a valid fern family. It seems as though every attempt to lay out a rational approach has led to a different set of circumscribed families and genera. Just look at all the abandoned genera in the list of Latin Names. It might even be said the fern families provide a better guide to pteridologists than to pteridophytes.

The Flora of North America in a chapter, Pteridophytes of North America, by Warren H. Wagner, Jr. and Alan R. Smith, lays out the problems in a section titled Classification---The Higher Ranks. One can sympathize with the difficulties, but still be dismayed by a lack of clarity or the provision of useful guidelines to identification.

So be it. Well, we need something in the way of classification; this site has chosen the FNA as its principal standard. With exceptions.

Here are the exceptions:

  • Dryopteridaceae. As defined by FNA, the family contains more than a dozen genera with no unique characteristics to set them apart. Elsewhere in the fern taxonomic world, this loose definition is replaced by a narrower collection, here limited to Arachniodes, Cyrtomium, Dryopteris, and Polystichum; even this group has few unifying features. Other FNA members comprise the Woodsiaceae, held together as deciduous, having two vascular strands within the darkened base of the stipe. In some floras and monographs, the Woodsiaceae are subdivided further, and the temptation to embrace something of utility to gardeners is strong.
  • At the genus level Oreopteris replaces Thelypteris for the species O. limbosperma, not in any case native to North America, and recognized as separate at the generic level by reason of an erect vs. creeping habit, scales vs. hairs on the stipe, and indusial differences.
  • At the species level the changes are due to common usage.
    • Polypodium polypodioides replaces Pleopeltis polypodioides.
    • Asplenium viride replaces Asplenium trichomanes-ramosum .

All in all, it is probably practical for the fern enthusiast to regard the fern families with a grain of salt, and focus on the genera and species directly. It might also be noted that this is far from heretical; the major fern horticultural references downplay or ignore the families.

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