Ferns in Ontario

Ferns are some of the most intriguing plants I have come across while conducting field surveys in central Ontario. They are living fossils! Ferns appear in the fossil record nearly 360 million years ago. This is long before the evolution of land animals (including dinosaurs) and nearly 200 million years before flowering plants evolved. Since ferns predate flowering plants, this means that they do not produce flowers or seeds. Reproduction in ferns is instead aided by the production and release of tiny spores into the environment.

Ontario is home to approximately 75 species of fern. Some are very common, while others are extremely rare and only found in specialized habitats such as limestone rock crevices. Telling some fern species apart can be a challenge for some people. However, most species are quite recognizable and easy to identify.

Fern identification diagram.
Simple key identification sketch for fern identification (Drawing Credit: Candice Talbot, 2019).


The following are some common examples (but are not limited to) of ferns that are found in Ontario. If you want more information please see the references section below.

Christmas Fern (Polystichum acrostichoides)

The festive name of this species can be attributed to its evergreen leaves, which remain green year-round and can even be used as Christmas décor. As you can see, the Christmas Fern has straight pinnae and no pinnules. Interestingly, the sori only appear on the upper portion of pinnae, instead of all of them.

Side-by-side photos of a fern.
Christmas Fern. On the left, the topside of the fern. Note the lack of pinnules. On the right, the underside of the fern. Note the dots. The dots are the sori, which only appear on the undersides of the final sets of pinnae (Photo Credit: Candice Talbot, 2019).

Mackay’s Brittle Fern (Cystopteris tenuis)

Named after Victorian botanist Alexander Howard Mackay (the link provides a list of his works) in 1875, this tiny, delicate fern species is usually found in shady rock outcroppings and cliff faces. They can also be found on the forest floor. Unlike the Christmas Fern, this species has definite pinnules, and the sori appear on all set of pinnae, hugging the margins of the pinnules.

Side-by-side photos of Mackay'a fern.
Mackay’s Brittle Fern. On the left, entirety of this small fern species. On the right, the underside of the fern, showing sori. (Photo Credit: Candice Talbot, 2019)

Marginal Wood Fern (Dryopteris marginalis)

This is a common species found in a variety of forested habitats in scattered, loose clumps. The word “marginal” in the common name of this species refers to the sori. The sori appear neat and evenly spaced along the margins of the pinnae.

Side-by-side photos of Marginal Wood Fern.
Marginal Wood Fern. On the right, a forest floor covered in clumps of marginal wood fern. On the left, the underside of the fern, showing the evenly spaced sori along the margins of the pinnae. (Photo Credit: Candice Talbot, 2019)

Resources for Identifying Ferns

There are many resources available which can help you in your quest to identify a fern species. In print form, I enjoy using the following:

  • Peterson’s Field Guide to Ferns of Northeastern and Central North America by Boughton Cobb, Elizabeth Farnsworth and Cheryl Lowe
  • Ferns and Fern Allies of Canada by William J. Cody and Donald M. Britton.

Internet resources exist too, such as:

  • Ontario Ferns (Website run by Walter Muma)
  • iNaturalist Ferns of Ontario (You can add your own fern photos to this citizen science website, and if you are having real difficulty identifying a species, there is always an expert around to help you. In fact, the crowdsourcing software on the website may even identify the species for you!)

Now that you have been introduced to these fascinating and diverse plants, you can get out there and begin your own fern identification journey.