Ferns Unfurling into the Future

Since spring is the time of transition, this blog is transitioning too.  It is time for my final outdoor classroom blog post.  Next time, I will return to my original "Biological Thinking" blog of discovering biological phenomena in everyday encounters with nature.  I hope you stay tuned if you have enjoyed my site-specific posts.  Thank you for reading!

A Fern Leaf

Our final topic: ferns.  Ferns are so common in the South that it is easy to overlook their strange beauty.  In the summer, many people display ferns in baskets outside their homes or apartments.  If you walk through the woods, ferns contribute to much of the background green of the understory.  Their repetitive intricate form makes them ideal for adding greenery to bouquets.  They are so familiar, yet they are so unusual. 

Fern spore-producing structures called sporangia.

Most plants we know of produce flowers and seeds to grow their offspring.  Seeds are tiny plants with a starter food supply wrapped in a protective coating.  They are produced from flowers.  When a seed grows, the tiny plant in it gets larger until it is a hackberry tree or a clover plant or, well, you get the idea.  Ferns, however, do not make flowers or seeds.  Fern plants make spores.  Spores are microscopic bits that are so light they can blow for miles on the wind.  When they land, if conditions are moist, they can grow into a small green leaf-like flat structure called a gametophyte.  The gametophyte looks nothing like a fern - just a tiny green patch.  The gametophyte grows for a while on its own, then it produces structures that can grow into a full-grown fern.

It's difficult to find gametophytes, but its easy to find spores.  Just look for dots on the bottom sides of fern leaves - those are pockets filled with microscopic spring-loaded spore-launchers called sporangia.  If you could shrink yourself, you could hang out under a fern leaf just for the fun of watching the tiny sporangia catapult their spores.  Nature's microscopic fireworks!

How leaves of flowering plants open up.

Another difference between ferns and flowering plants is how their new leaves open up.  The above plant, a flowering plant, has new leaves that are enlarging and opening by unfolding.  The young leaves are small and creased, the mature leaves are open and flat.  Below you see a fern leaf opening up.  Young fern leaves are small and curled up.  When they grow, they unfurl or unroll.  Young fern leaves look like the tops of violins (also called fiddles), so young fern leaves are called fiddleheads.  Fiddleheads might be green or brown or hairy or look quite different than the leaves they mature into.  It's easy to find fiddle heads in the spring and early summer - just look around the base of fern leaves, which we have in abundance all over our outdoor classroom.

Fern fiddlehead with a spore-producing leaf behind it.

There is a term for the unfurling of fiddleheads, of course, since there is a term for everything in science.  It is perhaps my favorite scientific term: circinate vernation (pronounced SIR-sun-ate ver-NAY-shun).  Look at the first word: circinate.  What other word starts with circ-?  Circle!  Circinate means circling or spiraling.  The second word might be tougher to figure out.  It derives from the word 'vernal', which means spring.  So circinate vernation is literally the unfurling of the spring, which is what ferns do.

More fern fiddleheads.

Ferns are ancient plants on earth.  Well, the plants in our outdoor classroom plant beds aren't ancient - they are the same age as their flowering neighbor herbs.  What I mean is that ferns were present on earth before flowering plants evolved.  They were some of the earliest plants in the fossil record, and they used to be the dominant type of plant on earth.  Now ferns are all fairly small plants, but before there were trees like we have now, ferns could be any size up to as large as small trees.  Ferns spores are a limitation that requires moist habitat, so ferns can't grow everywhere.  When some plants evolved the ability to form flowers and seeds, they could live in many types of habitats, so the flowering plants out-competed the ferns and became the dominant types of plants on earth. 

This fern leaf is almost completely unfurled.

All plants, including ferns, use photosynthesis to capture the sun's energy and make food.  Like flowering plants, ferns have xylem and phloem vessels for transporting food and water.  There are even more simple and ancient plants still easily found, even in our outdoor classroom: the mosses.  Take a look at the plants covering the rocks behind with waterfall.  They are mostly mosses, which don't have flowers, seeds, xylem or phloem.  They still photosynthesize, and they make spores like ferns do.

Moss - an even simpler plant than ferns.

If you want a more ancient plant than moss, you have to look into the pond at the algae.  Which brings us back to the very first topic we started with in August! 

I will leave you with one last picture of a fiddlehead getting ready to open up and live its life in the world.  It's so full of possibility!

A young fiddlehead.

Mosses, Lichens and Succession

Life has a way of taking over here on Earth.  Any surface without living things on it will eventually have life growing on it if you wait around long enough.  A new sidewalk of poured cement will have plants growing through cracks after twenty years.  New roofs will eventually become soft and covered with mold, moss and even plants.  Fresh lava from a volcanic eruption will cool, harden and in several decades be covered by a forest (Neat example here).  The invasion and growth of life on nonliving surfaces is called succession, and it's happening right here in our classroom.

Green and grey lichens growing on rock.

The nonliving surfaces we have at the classroom are mostly the rocks.  The big boulders and the flat rocks around the pond are too recently dug from the ground to have life on them yet, but they probably will by the time you graduate from high school.  The rocks with the waterfall behind the pond and the rocks that make up the wall at the back of the classroom have been exposed at the Earth's surface for long enough to have some neat life growing on them. 

Organisms that can colonize bare rock are called pioneer species.  Lichens are usually the first pioneer species, and they look like color splotches on the surface of rocks - white, green, grey, yellow or even orange.  Lichens are actually two organisms for the price of one: a fungus and an alga living together.  The fungus and alga form a mutualism - an interaction where both organisms benefit.  If you remember from the beginning of the year, algae grow in our pond - algae can only live where they don't dry out.  In lichens, they live surrounded by cells of fungus so they can live outside of a pond.  In return for this good protection, the algae provide the fungus with food from doing photosynthesis.  Together, the organisms that form lichens make acids that slowly dissolve the rock on which they grow, which makes tiny crevices in the rocks.

White, green and grey lichens plus dark green mosses growing on a rock.

Once lichens have been growing on rocks for a while, mosses are able to survive there too.  Mosses are plants that don't have flowers or stems or roots - just tiny green leaf-like structures and microscopic hair-like structures.  Mosses send their hair-like structures into the crevices the lichens made in order to anchor themselves on the rock.  Then the mosses grow bigger.  They die back during harsh weather and grow more in good weather.  As they die back, their dead parts decompose in place, and they turn into a tiny bit of soil.  After several years, mosses build up enough soil underneath themselves that other plants can move in.  Mosses can also start to grow in cracks and pockets in rocks.

Just as mosses build habitat for small flowering plants, the flowering plants provide habitat and food for more creatures.  Flowering plants have roots that hold the soil in place, and they also add to the soil as they die back each winter and decompose.  Mosses and plants can host tiny insects, adding to the variety of life growing on a formerly bare rock.  As the years go on, the soil builds and builds and larger plants, shrubs and eventually trees can grow on what was once bare ground.  Eventually a mature forest might be found where once there was bare rock, and succession has been a success.

A rather large moss behind the waterfall.

Next time you are near an older neighborhood or a vacant lot in Nashville, see if you can recognize succession.  Old houses have mossy roofs.  Ancient stone walls are covered in plants with trees growing through them and lizards living between the stones and roots.  Old parking lots or yards are infiltrated with weeds and dotted with butterflies drinking from the weeds' flowers.  You can see the results of succession at the River Campus too.  Most of what is now the wetland used to be an open farm field with only grass - only 15 years ago!  Now it has grown into a young forested wetland with lots of plants and small trees.  Life certainly does take over!

Green Algae

The school where I work has an outdoor classroom that invites nature into our urban schoolyard and creates a peaceful outdoor space for students to learn about life.  We have trees, wildflowers, and a pond, each hosting their share of associated organisms.  I'll be doing some nature blogging about the outdoor classroom for use by teachers at our school, and I'm posting the first outdoor classroom blog post here:

Welcome!  I'm excited about starting an outdoor classroom blog.  I can't wait to see what we find in our little urban nature oasis.  The subject of our first post is green algae.

If you look under the surface of the pond, you see a very busy ecosystem indeed!  There are plants, fish and insects, and those are just the visible organisms.  There are way more microscopic organisms than big ones, which I'll save for a future post.

Green algae growing just below the surface of our pond.

The strangest macroscopic (big enough to see) organism is the filamentous green alga that forms clouds of soggy green cotton candy.  But what on earth are green algae?  They seem a lot like plants: they photosynthesize, they have cell walls, and they have chloroplasts (green structures that photosynthesize).  There are also some features of green algae that we don't usually associate with plants: they live entirely under water; they don't form roots, leaves or stems; and some of the microscopic ones can swim!  Scientists have wavered a bit about whether algae are actually plants or protists.  The discovery of how to sequence DNA has allowed algal geneticists to confidently classify green algae as plants, though the other colors of algae (red, brown and blue-green) are not classified as plants.  I have had to re-learn my green algae taxonomy!

Interconnected strands of green algae pulled up from under the surface.

Our green alga (alga, hard g, is singular, and algae, soft g, is plural) is a filamentous type, meaning it grows in long strands.  The filaments (strands) of green algae are only one-cell thick, which is surprising considering how tough they are.  Each algal cell is cylindrical like a soup can, and the filament is arranged like an infinite strand of soup cans glued end to end.

Green algae out of the water.

The color of green algae comes from the pigment chlorophyll, just like in other plants.  Chlorophyll is the molecule that can catch light to allow plants to use its energy to build food.  Green algae cells contain structures called chloroplasts that hold the chlorophyll plus all the other machinery needed to conduct photosynthesis.  All plants' cells contain chloroplasts.

I looked at the algae from our pond using a microscope that magnified what I saw by a factor of 100.  In the picture below, you can see the cell wall between adjacent algal cells, just above the pointer.  Cell walls are rigid structures made of cellulose (a strong, rigid molecule), and they give plant cells their shape.  Paper is made by starting with plant material and getting rid of everything but the cellulose, meaning that paper is essentially squished, dried plant cell walls.

The pointer rests on a filament of green algae.  A broken alga releases its cell contents. 100x

Another interesting thing in the picture above is the broken cell.  A chloroplast is slipping out of the broken plant cell in the center of the picture.

Below is another view under the microscope, with one normal filament and one filament with shrunken cell contents.  The chloroplasts and other structures have been compressed into a central structure in each cell.  The strange filament may be undergoing reproduction or it could be stressed, but either way, you can see the beautiful cylindrical shape of each individual cell.

Shrunken cell contents in the lower filament allow you to see the cell walls.  The round object is an air bubble. 100x

In our pond, the algae seem to be growing quickly.  There is ample sun for food, plus decomposing leaves and insect/fish excrement providing nutrients, the equivalents of vitamins in our food.  When you see a pond with lots of algae in it, you can assume that there are a lot of nutrients in the water, either from natural sources or from pollution.