Dark Dwellers: Ferns of the Corkscrew Cyprus Swamp Preserve

In the steamy, shadowed recesses of the Corkscrew canopy grow the dwellers of the dark. They seem oblivious of the surrounding giants. The crowns of Cyprus trees tower 10 stories overhead. They struggle for hundreds, sometimes thousands of years seeking the light. The ferns are old too but not as individuals. Their species far outstrips the antiquity of the Cyprus species. They have been around for 350 million years. They are more than twice as old as Cyprus.*

The featured image shows two fern varieties. In the dark of the swamp these are easily identified by the two types of fronds. One is the shiny surface of the Giant Leather (Acrostichum danaeifolium) and the other is the non-branching Long Strap (Campyloneyrum phyllitidis). 

There are at least 25 fern varieties in Florida. What we see here is only a fraction of the diversity of the fern. It is estimated that globally there are 10500 living species. That is four times the combined number of gymnosperms and lycophytes. They are second in variety only to the angiosperms. They are important because they are very efficient at carbon fixation and soil stabilization. The carbon-based energy industry of today is based almost exclusively on the deadfall of millions of years of fern life cycles. These plants lived and died in the anoxic swamps of the Permian (250 mya) and Cretaceous (135 mya) periods. In the Cretaceous period giant, angiosperm-dominated rainforests that developed in the tropical environments.  Ferns were able to successfully exploit and diversify in these new ecosystems without competing with the flowering plants. This is probably why today most species of ferns grow in the tropics. When walking through the Corkscrew Preserve in SWFL you should imagine yourself walking in a Cretaceous period swamp. The only thing missing would be the giant reptilian dinosaurs of which we have only two small versions remaining in Florida, the alligator and crocodile.

There is another more basic reason for the swamp ferns to prefer the damp environment. The gametophyte stage of their reproduction depends on water to transport the sperm to the egg to produce cells of new plants outside of the parent fern plant. The sporophyte stage part is easy to see and feel. In this essay we will pay careful attention to just sporulating portion of fern reproduction. For a reference to the full cycle please look at the illustration at the end of this posting.

There are two commonalities running through all of the ferns. They are chlorophyl metabolism based, non-seed-bearing plants with true vascular systems and they have a two stage reproduction cycle. Ferns are very primitive plants with complex reproductive cycles. There are two methods. One is through budding and the other is through sporulating. Budding is simple asexual reproduction. Sporulating is a much more interesting method and this essay will pay some attention to the early steps of this second method. 

Unlike angiosperm or gymnosperm plants, ferns do not use flowers or seeds for reproduction. As a refresher, please recall that flowering plants use sexual reproduction methods with pollen and ova. (See previous essay on Bauhinia Trees). Ferns use a two-step process for reproduction. The large green plants that are seen with fronds of leaves are the first stage of reproduction called a sporophyte. This stage has a full complement of DNA and is therefore a sporophyte diploid plant. The first stage produces spores that may be either male or female. Spores must land on a suitable surface, such as a moist protected area to germinate and grow into gametophytes. The gametophyte grows into a small plant about a half inch square area. The gametophyte makes sperm and eggs which join together on wet surfaces to generate a new sporophyte. In this essay we will pay most attention to just the sporulating portion of fern reproduction. They may be either male of female.

While walking through the understory of the Florida preserve areas one could easily see and feel many ferns of at least 24 types. Three of these are demonstrated here, the Long Strap fern, Wart fern, and the Southern Sword fern. These are not easily identifiable, however, using the University of Florida plant identification web site.*** I found the best ID match.

Long Strap Fern (Campyloneurum phyllitidis)

Wart fern (Microsorum scolopendrium)

Southern Sword Fern (Nephrolepis biserrata)

It is easy to recognize the similarities in these plants. They all have a chloroplasts, circulatory system, sporangium, and spores and a common two stage reproduction method. 

There are parallels with other plants. The microsporangia of the angiosperm flowers develop in the anther of the stamen. For them, microspores produced within the microsporangia (stamen) of which there is usually four per anther, eventually develop into pollen grains. Fungi, horsetails, mosses, worts and ferns all produce spores. It is complicated but it works. 

Ferns are beautiful and intriguing. If the ferns had been very important for food or industry, they might have been exploited like the threatened Florida bald Cyprus. Be sure to see the previous publication, Earth’s Axial Tilt Determines Forest Winners. Watch for the future posting on gametophyte portion of fern life.

As Nick, one of our followers, stated “May the Forest Be With You”. To that I add “Welcome to the Dark Side of the Forest.”

References:

• “Distribution of living Cupressaceae reflects the breakup of Pangea” by Kangshan Mao, Richard I. Milne, Libing Zhang, Yanling Peng, Jianquan Liu, Philip Thomas, Robert R. Mill and Susanne S. Renner, 1 May 2012, Proceedings of the National Academy of Sciences.
  DOI: 10.1073/pnas.1114319109

**About Ferns, Pinson J,

*** University of Florida Plant identification UF/IFAS

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