The first lineage of plants to develop a true vascular system, ferns came to dominate and colonize the mid-late Devonian landscape about 400-360MYA. Lycopods, which are not ferns, but cousins, evolved earlier during the Silurian ~440MYA and have a proto-vascular system.
Before ferns, there were mosses, lichens, algae, and fungi scattered about and nothing tall grew on the landscape. The tallest primitive plants grew to be about 2’ tall, and the landscape looked much like what Iceland looks like today--rocky, covered with moss, and not a lot of topsoil or organic matter. Ferns are different from mosses in that they have developed true roots, and xylem and phloem to transport water and materials throughout the plant. This vascular system allowed ferns to tower over mosses and grow to heights never before seen on earth--growing above 2’ was a big deal.
With a vascular system to organize water absorption and storage, ferns got bigger and colonized more environments previously uninhabitable by mosses. Hills, cliffs and mountains that were too dry for mosses were easily inhabited by ferns, and helped to keep these previously dry places moist enough to expand moss’ range. With the help of ferns, plants finally spread in-land. Around 360MYA, the landmasses of the earth collided, forming the supercontinent Pangaea. Ferns spread throughout Pangaea, covering it almost entirely and is the reason why ferns exist and have existed on all land masses. With a lot of space comes a lot of ecological niches, which results in a lot of diversity. Fern diversity exploded about 360MYA, at the beginning of the Carboniferous Period, rightly dubbed “The Age of Ferns”.
In older botanical classifications, the term “Fern Ally” refers to other proto-vascular plants that evolved alongside ferns. Most Fern Allies are extinct, though a rare few survive today. Most ferns that have evolved are extinct as well, due to shifts in earth’s climate over the millenia.
THE AGE OF FERNS
The Age of Ferns was a period of change for both the earth’s landscape and climate. Great swamps and forests of ferns and other plants dominated the planet. Most of the planet at that time was warm and tropical. With ferns covering more of the landscape, and general plant populations increasing, they caused the atmosphere to change as well. During the Carboniferous Period, there were so many plants that the oxygen level of the atmosphere increased from ~15% to ~35%. Carbon dioxide levels fell by about the same amount--all of that free carbon was fixed by the plants into themselves, and eventually the soil. Talk about green living.
It was during the Carboniferous Period that most of our coal and oil deposits were formed. Sea levels would rise and fall, covering great swamps of plant life with sediments. The sediments built over time, crushing the plant matter under immense pressure, forming coal and oil. That’s right, coal and oil come from dead plants--particularly dead ferns and fern allies--not dead dinosaurs. Although, they still make for cool archaeological discoveries. The removal of the greenhouse gas and carbon dioxide caused a drop in the climate of the planet, and it spurred an ice age at the end of this period.
Although there were a few miniature ice ages throughout the Carboniferous Period, none were as cold or as powerful as the last ice age of the period, about 300MYA. Grab your gloves--this ice age wiped out most fern species, although a few survived into the Permian Period.
They did not immediately spread out and diversify after the mass extinction. Most extant ferns actually evolved much later, during the Cretaceous Period, after flowering plants existed (about 100-70MYA) . Why? The ferns that survived the Carboniferous-Permian extinction were all high-light loving plants. However, the canopy was dominated with taller gymnosperms and seed plants towered over the landscape, shading most of the ferns. The fact that the Permian was much drier restricted fern radiation (spreading and diversity) until about 200MYA. In an attempt to compete with gymnosperms, some ferns evolved into tree ferns (Cyatheales) retaining the ancestral need for full sun, but unlike other ferns, grow into trees to reach for the light. Other fern growth was restricted due to shading from taller plants.
Then, in the Cretaceous, ~100MYA, a seperate lineage of ferns caught a lucky break. A horizontal gene transfer from a moss is what is believed to have saved the ferns . Plants exchange genes with the organisms that grew closely and around them, vectored by gene-transferring bacteria and fungi. A bacteria likely took the gene for making a special protein called Neochrome from a moss, and inserted it into a fern ancestor.
Why is Neochrome key? Well, it allows ferns to make use of shade or indirect light by increasing productivity from using red and far-red light. Plants mostly use red and blue light, some yellow, some UV, and almost no green light. In a shaded understory--the place where plant life grows beneath the forest canopy, where only a small percentage of light penetrates--the blue light is mostly captured by the tallest plants and does not bounce or bend well. Red and far-red light remains to bounce farther down in a higher ratio than blue light. Understory plants that can make good use of what light is available are more successful than the ones who can’t, and it’s this adaptation that allowed the ferns to conquer the understories of many environments. In addition, these ferns (Polypodiales) have adapted to other niches as well--some even becoming epiphytes, like the staghorn fern (Platycerium). Others, like the bird’s nest fern (Asplenium), have adapted well to darker understories, and incidentally, to the lower light of indoor environments as well.
In Victorian Era Britain, there became an obsession with ferns. England’s cool, moist, foggy climate made it perfect for growing ferns and many people added ferns to their gardens and houseplants--a new concept in the Western World at the time. It wasn’t until the discovery that ferns reproduce by spores that they were able to be commercially produced. Until that time, when a fern died, a replacement had to be taken from the wild (something we do not recommend doing, ever).
The combination of spore propagation, along with the advent of the Wardian Case, the world’s first glass terrarium, allowed easy care of ferns indoors. The Wardian Case also made Orchidelirium a craze at the same time. Fern collecting transcended social class and barriers at that time and the aristocracy even encouraged the lower classes to “lift themselves up” by collecting ferns. Even then, they knew plants make all people happy. The first glass houses appeared and growing plants indoors became a pivotal symbol of quote, “man’s triumph over nature” and shifted how society saw itself and its relationship to nature. We were no longer subject to the whims of nature, and this changed the philosophy of the late 19th and early 20th centuries.
FERNS: THE FACTS
Ferns do not flower, but reproduce by splitting, rhizomes, and spores. Species of ferns within the fern family Polypodiaceae are generally tropical, medium-light plants. Other ferns from other families can be treated similarly, though not all. Ferns have been known to purify the air, retaining ancestral genes from when the earth’s atmosphere was more unfavorable than it is today. Although ferns get a bad reputation for being finicky, by looking at their evolutionary journey, it’s evident these ancient survivors are tough and can thrive, so long as their basic needs are met. Ferns are generally hassle-free. They also tend to grow faster than other tropical plants if they’re getting enough light. Ferns are famous for being able to completely regrow from the crown, so if the leaves are damaged, you can take them off and the fern will replace them relatively quickly. The fast regeneration coupled with their air-purifying properties makes them one of our favorite plants.
Thrives in medium to bright indirect light. Some Ferns, like the Bird's Nest Fern, can tolerate low indirect light.
Water every 1-2 weeks, allowing soil to dry out halfway down between waterings. Expect to water more often in brighter light and less often in lower light.
Does best in higher humidity.
65°F-85°F (18°C-30°C). It’s best not to let it go below 60°F (15°C). If temperatures swing too low, some ferns like the Boston Fern may go deciduous.
Sensitive to humidity, but otherwise a very easy-going plant. May get scale and mealybugs. Treat scale bugs and mealybugs as soon as they appear with weekly sprays of horticultural oil. Crisping tips may indicate either low humidity or that the plant is too dry.
SYMPTOM: Pale green leaves, dry potting mix
CAUSE: Thirsty plant, underwatered
SYMPTOM: Yellowing lower leaves, wet potting mix
Generally not harmful to pets upon consumption. Best practice is always to keep houseplants out of reach of small children and pets.
Words By The Sill
Empowering all people to be plant people — a collection of articles from The Sill’s team of Plant Experts across a variety of plant care topics to inspire confidence in the next generation of plant parents. Welcome to Plant Parenthood™.