Swamp Fern has Three Tricks Up Its Stipe

28 Dec

Blechnum serrulatum (Telmatoblechnum serrulatum)

(Blechnon is  Greek for fern.  Serrulatum refers to tiny toothlets on the leaf margins. Telmato denotes wet habitats.)


Blechnum serrulatum 5.jpg

Swamp fern by John Bradford

There’s nothing more enchanted than bright morning in a cypress swamp during the dry season.   The habitat is open, easy to navigate, bugless, and decorated with colorful lichens from rose to battleship gray, asters in bloom, and mossy hues a Leprechaun might recognize.

Taxodium above water line

The biology is enchanting too, seeing cypress knees with spongy growing tips; seedlings seizing the day under the leafless canopy; northern needleleaf with ants; and a dozen plant species huddled on the bald cypress above the highwater line.

Tillandsia albisiana plant

Northern needleleaf with ant

Tillandsia balbisiana ants

So many wonders, yet time and space force a choice.  Swamp fern looks like “any old” fern, so what’s swampy about it?   The fern shows at least three curious adaptations to life with its roots submerged some months and desert-dry other months.   Being equipped for both extremes give the species a competitive edge, in charge where purely aquatic plants would fry and where purely dry-land plants would drown. Sun or shade just fine.

Blechnum sori

Swamp fern. Two rows of spore cases beneath the toothy leaflets.

Wet and Dry Adaptation 1.   The leaf stalks have veins embedded among air pipes extending from the high dry leaves down into the intermittently submerged regions.

Blechum stipe section magnified

The leaf stalk cut and magnified.  The well protected veins are white, surrounded by the air pipes.

Wet and Dry Adaptation 2. When the fern perches on a bald cypress above the high-water line, the plant is not permanently an epiphyte unable to reach the earth.  Look closely…like a little banyan, it drops rhizomes and roots from its elevated base down along the cypress trunk and into the soil at the host tree’s base.

Blechnum on bald cypress

Swamp fern hanging on bald cypress.  The fern’s rhizomes and roots descend from the attachment point to the ground.  Some months they would be largely submerged.

Wet and Dry Adaptation 3.  This one requires speculative interpretation.  When the fern sits directly on periodically flooded mud it can build itself a pedestal made of a vertical cluster of slender rhizomes bound together into a spongy fascicle by a fibrous meshwork of roots.

Blechnum trunk on ground 1.jpg

Base of the fern (leaf stalks on top) rising from the black pedestal.

The pedestal lifts the fern above the flood when necessary, and looks like it collects debris and microbes in its network of nooks and crannies.  When the water is low, the pedestal becomes a reservoir of moisture and nutrients.

Blechnum trunk mid distance

The pedestal is a mass of vertical rhizomes and roots all tangled together to make a tall sturdy sponge.

Among the blackened dead yet fibrous roots are living roots looking like they harvest water and nutrients from the spongy pedestal through which they creep.

Blechum living root magnified

Magnified view of living root creeping through the blackened spongy matrix of the pedestal.


Posted by on December 28, 2018 in Swamp Fern, Uncategorized


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5 responses to “Swamp Fern has Three Tricks Up Its Stipe


    December 29, 2018 at 9:39 pm

    Hey George,

    Very cool piece on the swamp fern.

    BTW, I hope that when the day comes that you retire, that you’ll continue these wonderful blogs. 😊

    BTW, one of my students who took a recent FL Master Naturalist course was hoping to take your spring class. I hope he got in – nice young man – Dane Boggio.

    Wishing you a great 2019!


    • George Rogers

      December 31, 2018 at 11:10 am

      Hi Chris, Nice to hear from you. I’m sure Dane can get in. The class filled and then was expanded a couple times. If he tried while it was full he may think he is blocked, but I added a second day i order to accommodate all takers, so no problem…and he is welcome to contact me for help.

  2. theshrubqueen

    December 29, 2018 at 10:20 pm

    I was so intrigued by the pictures I had to read the post twice!

  3. Russell Owens

    March 22, 2019 at 3:23 pm

    I saw a swamp fern in the Loxahatchee National Wildlife Refuge that had the sori spread apart with some distance from the axis. Does this happen often?

    • George Rogers

      March 23, 2019 at 10:08 am

      Well, not to my knowledge, but I’ve seen other major mutations in the leaves.


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