Fern

Fern, or pteridophyte, is any one of a group of some twenty thousand species of plants. A fern is defined as a vascular plant that reproduces by shedding spore to initiate an alternation of generations, and forms new fronds by circinate vernation.

A group of plants that may be termed ophioglossoids was once considered to be true ferns, but is now known to be an isolated group. These include plants traditionally grouped in the family Ophioglossaceae, including adders-tongues and grape-ferns. These are now considered to be "fern-allies."

Life cycle

Fern's life cycle consists of two distinct stages:

1. Sporophyte: a macroscopic plant

   produces asxeual spores

2. Gametophyte ("prothallus" specifically for fern): a microscopic heart-shaped entity

   produces sexual gametes

A typical life cycle:

1. Sporophyte produces spores
2. Spores develops into a gametophyte
3. Gametophyte produces gametes
4. Male gamete fertilizes female gamete
5. The fertilized gamete grows into a sporophyte

Structure

A sporophytic fern contains

• Frond[?] ("fern leaf"): green, photosynthesizes
  • When younger, it is curled into a fiddlehead[?]
  • contains spores
• Petiole: stem[?]-like
• Rhizome: root-like, underground, absorbs nutrients, anchors

A gametophytic fern contains:

• Thallus[?]: green, photosynthesizes
  • contains gametes
• Rhizoids[?]: root-like
• No stem of any kind

Classification

Ferns have traditionally been grouped in the class Filices, but some modern classifications assign them their own division in the plant kingdom, which may be known as Pterophyta or Filicophyta. This may be subdivided into four main groups, or classes (or orders if the ferns are considered as a class):

• Marattiopsida
• Osmundopsida
• Gleicheniopsida
• Pteridopsida (or Filicopsida)

The last group includes most plants familiarly known as ferns.

A more complete classification scheme follows:

• Kingdom: Plantae
  • Division: Pterophyta
    • Class: Marattiopsida
      • Order: Marattiales
      • Order: Christenseniales
    • Class: Osmundopsida
      • Order: Osmundales (the flowering ferns)
    • Class: Gleicheniopsida
      • Subclass: Gleicheniatae
        • Order: Gleicheniales (the forked ferns)
        • Order: Dipteridales
        • Order: Matoniales
      • Subclass: Hymenophyllatae
        • Order: Hymenophyllales (the filmy ferns[?])
      • Subclass: Hymenophyllopsitae
        • Order: Hymenophyllopsidales
    • Class: Pteridopsida
      • Subclass: Cyatheatae
        • Order: Cyatheales (the tree ferns)
        • Order: Plagiogyriales
        • Order: Loxomales
      • Subclass: Schizaeatae
        • Order: Schizeales (including the climbing ferns)
        • Order: Marsileales (the water-clovers, mosquito fern[?], water-spangle)
      • Subclass: Pteriditae
        • Order: Lindseales
        • Order: Pteridales (including the brakes and maidenhairs)
        • Order: Dennstaedtiales (the cup ferns)
        • Order: Hypolepidales (including bracken)
      • Subclass: Polypoditae
        • Order: Aspleniales (the spleenworts)
        • Order: Athyriales (including the lady ferns, ostrich fern[?], maiden ferns, etc.)
        • Order: Dryopteridales[?] (the wood ferns and sword ferns)
        • Order: Davalliales (including the rabbits-foot ferns and Boston ferns)
        • Order: Polypodiales[?] (including the rock-cap ferns or Polypodies)

Economic Uses

Ferns are not as economically important as, say, cereal grains, with one possible exception. Ferns of the genus Azolla, which are very small, floating plants which do not look like ferns, and are called mosquito fern[?], are used as a biological fertilizer in the rice paddies of southeast Asia.

Other ferns with economic significance include:

• Dryopteris filix-mas -- male fern[?], used as a vermifuge[?]
• Rumohra adiantoides -- floral fern, extensively used in the florist trade
• Osmunda regalis and Osmunda cinnamomea -- royal fern and cinnamon fern, respectively, the root fiber being used horticulturally; the fiddleheads of O. cinnamomea are also used as a cooked green
• Matteuccia struthiopteris -- ostrich fern, the fiddleheads used as a cooked green in North America
• Pteridium aquilinum -- bracken, the fiddleheads used as a cooked green in Japan
• Diplazium esculentum -- vegetable fern, a source of food for some native societies
• tree ferns, used as building material in some tropical locales

In addition, a great many ferns are grown horticulturally.