Fern ally Wednesday, June 24, 2009

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Lycopsida

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.

Classification

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"):

Equisetum fluviatile from the Equisetopsida (horsetails)

• 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:

Psilotum nudum from the Psilopsida (whisk ferns)

• 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)

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.

Relationships

Isoëtes 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.)

External links

• Common Ferns and Fern-Ally Species
• A Classification of the Ferns and Fern-Allies (uses frames)
• Non-seed plant images at bioimages.vanderbilt.edu
• Lord, Thomas R. (2006). Ferns and Fern Allies of Pennsylvania. Indiana, PA: Pinelands Press [1]