Ferns: The Emergence of Roots and Stems

Introduction

In the previous tutorial we discussed
lycophytes,  which were the first vascular plants on earth.  

But these still did not closely resemble  the modern plants we are most familiar with,  

like trees. The next type of vascular  plants to evolve were finally of a  

more familiar form, and those were ferns. Ferns are more advanced vascular plants than those  

Ferns

we’ve discussed previously, namely because they  are the first to have true roots and stems. Fern  

stems bear leaf-like structures called megaphylls,  which are essentially larger versions of the  

microphylls grown by lycophytes. The fern group is  large and unbelievable diverse, including a variety  

of ferns and scouring rushes or horsetails.  Most fern species grow as small or medium-sized  

Fern Species

herbaceous plants, meaning no woody stems above  the ground, but larger tree ferns can be up to 25  

meters tall. The smaller herbaceous ferns can grow  as epiphytes, which again are plants that grow on  

other plants, and they can also be epipetric,  which is a term for plants that grow on rocks.  

The oldest ferns appeared during the  Carboniferous period, about 360 million years ago,  

but most modern fern groups appeared during the  Cretaceous period, about 145 million years ago. 

In ferns, like lycophytes, the diploid sporophyte  is the dominant generation, or the generation that  

we’re most aware of seeing. If you look at the  back or undersides of the megaphylls on a fern  

sporophyte, you’ll often see small brown or black  dots in neat rows. These brown dots are sori,  

or groups of sporangia where the haploid spores  are produced through meiosis. Spores are released  

from the sporangia, where they fall to the  ground and germinate as new haploid gametophytes.  

Not much is known about fern gametophytes in the  wild because they are very small and ephemeral,  

meaning they don’t live very long. Most of  what scientists know about fern gametophytes,  

also known as prothallia, comes from studying them  in a laboratory setting. The haploid gametophyte  

attaches to the soil with rhizoids. As with  the other gametophytes we’ve discussed,  

a fern gametophyte bears both reproductive  heads and can self-fertilize.  Antheridial heads  produce sperm cells through mitosis,  

and archegonial heads produce  egg cells, also through mitosis.  

When there is sufficient water in the environment,  the sperm cells can swim to the archegonial heads  

and fertilize the egg cells. Once an egg cell has  been fertilized, then it germinates into a new diploid  

sporophyte directly from the gametophyte. Once  the sporophyte is ready, the gametophyte dies off. 

Fern Sporophyte Generation

The fern sporophyte generation is readily  identified by the characteristic “fiddlehead”  

of its curved stem before the megaphylls unfurl.  Many people eat fiddleheads, but it’s important  

to properly identify the fern species first  because some are poisonous. Once established,  

Fern vegetative reproduction

many fern sporophytes are perennial, meaning  they will grow in the same spot year after year  

without having to alternate with the gametophyte  generation. Additionally, many fern sporophytes  

are able to engage in a different form of  reproduction called vegetative reproduction,  

which entails propagating new plants via rhizomes  growing in the soil. This reproductive strategy  

has caused a few species, like bracken fern, to  become aggressive weeds in some disturbed areas. 

Conclusion

And with that, we’ve covered both nonvascular  plants and the simpler vascular plants. Now  

it’s time to discuss the more complicated and  more recognizable types of vascular plants,  

so let’s keep moving forward in  the evolutionary history of plants.