Fern Ally

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Fern ally is a general term covering a somewhat diverse group of vascular plants that are not flowering plants and not true ferns. Like ferns, these plants disperse by shedding spores to initiate an alternation of generations. There were originally three or four groups of plants considered to be fern allies. In various classification schemes, these may be grouped as classes or divisions within the plant kingdom. The more traditional classification scheme is as follows (here, the first three classes are the "fern allies"):

Kingdom: Plantae

Division Tracheophyta (vascular plants)
    Class Lycopsida, (fern-allies) the clubmosses and related plants
    Class Sphenopsida or Equisetopsida, (fern-allies) the horsetails and scouring-rushes
    Class Psilopsida, (fern-allies) the whisk ferns
    Class Filices, the true ferns
    Class Spermatopsida (or sometimes as several different classes of seed-bearing plants)

A more modern or newer classification scheme is:
Kingdom Plantae
    Subkingdom Tracheobionta
        Division Lycopodiophyta
            Class Lycopodiopsida, the clubmosses
            Class Selaginellopsida, the spikemosses
            Class Isoetopsida, the quillworts and scale trees
        Division Pteridophyta
            Class Equisetopsida, the horsetails and scouring-rushes
            Class Psilotopsida, the whisk ferns, adders'-tongues and moonworts
            Class Pteridopsida, the true ferns
        Division Spermatophyta (or as several different divisions of seed-bearing plants)

To view the complete classification of Kingdom: Plantae click here

Note that in either scheme, the basic subdivision of the fern allies is preserved, but in the most recent scheme only the Lycopodiophyta is not classified with the ferns.

Psilotum nudum
Psilotum nudum from the Psilopsida (whisk ferns)

Equisetum fluviatile
Equisetum fluviatile from the Equisetopsida (horsetails)
Isoetes lacustris, a quillwortIsoëtes lacustris, a quillwort

Another way of looking at it is:
Several groups of plants were considered "fern allies": the clubmosses, spikemosses, and quillworts in the Lycopodiophyta, the whisk ferns in Psilotaceae, and the horsetails in the Equisetaceae. More recent genetic studies have shown that the Lycopodiophyta are only distantly related to any other vascular plants, having radiated evolutionarily at the base of the vascular plant clade, while both the whisk ferns and horsetails are as much true ferns as are the Ophioglossoids and Marattiaceae. In fact, the whisk ferns and Ophioglossoids are demonstrably a clade, and the horsetails and Marattiaceae are arguably another clade. (Traditionally, three discrete groups of plants had been considered ferns: the adders-tongues, moonworts, and grape-ferns (Ophioglossales), the Marattiaceae, and the leptosporangiate ferns. The Marattiaceae are a primitive group of tropical ferns with a large, fleshy rhizome, and are now thought to be a sibling taxon to the main group of ferns, the leptosporangiate ferns.)