Ferns aren’t quite as showy as flowering plants, but they are beautiful and their biology is fascinating, according to my guest this week, evolutionary biologist Dr. Emily Sessa of the New York Botanical Garden. She is here to teach us all about ferns, from their history to their unique properties.
Emily is the Patricia K. Holmgren director of the William and Lynda Steere Herbarium at the New York Botanical Garden in the Bronx and the principal investigator of Sessa Lab at NYBG. She is also an adjunct professor of biology at Cornell University in Ithaca, New York, and at the City University of New York Graduate Center. She holds a bachelor’s degree from Cornell in ecology and evolutionary biology and a Ph.D. in botany from the University of Wisconsin–Madison. She took her studies even further as a postdoctoral associate in ecology and evolutionary biology at the University of Arizona.
Dr. Emily Sessa is the Patricia K. Holmgren director of the William and Lynda Steere Herbarium at the New York Botanical Garden in the Bronx and the principal investigator of Sessa Lab at NYBG.
Photo Courtesy of Dr. Emily Sessa
Research in the Sessa Lab focuses on plant systematics and understanding the evolutionary and ecological processes that shape plant diversity. Lab members work on projects around this central theme, including systematics, historical biogeography, physiology, and responses to climate change and mass extinction. The lab is strongly concentrated on the seed-free vascular plants: ferns and lycophytes.
Last year, Emily published “Ferns, Spikemosses, Clubmosses, and Quillworts of Eastern North America,” a book in the Princeton Field Guides series.
Anybody who wants to know more about any of these plants can pick up this field guide and have a clear understanding —and a Ph.D. is not required to appreciate Emily’s writing and observations.
“It’s a hefty book,” she says. “It’s sort of right on the edge of what you might want to throw in your pack and take out in the field with you, but it does cover all the ferns east of the Mississippi, from Florida to Canada.”
She wanted the book to be something her colleagues would want to use and give to their students but also be something that any lay person could pick off the shelf and use.
How Emily Became Fascinated With Ferns
Emily is originally from Putnam County, New York, north of New York City.
“I’ve always loved plants,” Emily says. “I’ve always been a science geek and just drawn to the natural world. I grew up actually not too far from where I work today at the New York Botanical Garden.”
She says she spent a lot of her childhood out in the woods. She was an only child and was often out running around on her own looking at plants. She always found ferns and mosses in particular to be beautiful.
“I was an ecology and evolutionary biology major, and I studied mosses in a lab as an undergraduate,” she says. “And the more I got to learn about the non-flowering plants — so things like ferns and all the bryophytes, which is the mosses and their relatives — the more I kind of felt like this group was like the underdogs.”
Everyone loves showy flowering plants, but non-flowering plants have amazing biology going on, she explains.
“Ferns in particular are fascinating for a lot of reasons,” she says. “Everything from their genomic properties — their genomes are quite bizarre and different — to their physiology. Physiologically, they behave quite differently from flowering plants.”
There are more than 10,000 species of ferns, and they do not all look alike and they do not all live in shady habitats where they have constant access to water, Emily points out.
The log fern, Dryopteris celsa.
Photo Courtesy of Dr. Emily Sessa
Plant Lineages
Flowering plants (angiosperms) and conifers and their relatives (gymnosperms) make up a group of plants known as seed plants (spermatophyte.)
While angiosperms and gymnosperms are closely related, like a brother and sister, ferns (Polypodiopsida) are more like a first cousin, Emily explains.
It’s easy to spot a flowering plant and mentally catalog it in the right lineage. With the fern lineage, it’s not always obvious.
“There’s a lot of things in the ferns that don’t look like your picture of what a fern would look like,” Emily explains. “There’s lots of weirdos and oddballs and things like that.”
The spikemosses, clubmosses and quillworts of Emily’s book title belong to another plant lineage that is even more distantly related: the lycophytes.
“In eastern North America, I think we’ve got about 60 species of lycophytes,” she says.
A common denominator among ferns and lycophytes is they are spore-bearing vascular plants. That means they reproduce via spores rather than seeds.
Quillworts (Isoetaceae) are strange plants that look like grasses and are entirely aquatic. Spikemosses (selaginella) are “very diverse in the tropics, but they’re also quite diverse in kind of colder habitats in the temperate regions,” Emily says. Clubmosses (Lycopodiaceae) include about 500 species also known as “wolf foot” because their roots or branch tips resemble wolf’s paws.
At the head of all these branches on the evolutionary chart are land plants, which evolved about 500 million to 600 million years ago. Before then, all plants were aquatic.
“Once plants made it onto land, then you start to get diversification and divergence in what we now call the land plants,” Emily says.
Mosses never evolved specialized tissue to circulate water so they diffuse water across their bodies. They are small plants so they can stay near water. Vascular plants, like ferns, do have specialized tissue to move water around.
Modern lycophytes have small leaves. “Lycophytes had their day in the Carboniferous period, and if you are someplace where your power is coming from burning coal, chances are that coal that you are burning is actually fossilized lycophytes,” Emily says.
Lycophytes don’t have what are called “true leaves,” but seed plants and ferns do. Emily says defining true leaves is a distinction in the way that the vascular tissue enters the leaf and the level of complexity of the vascular tissue.
“So to be a fern, you have to have vascular tissue,” she says. “So you have to have that specialized plumbing. … It’s all about moving water around.” (You may remember the terms xylem and phloem from biology class.)
All seed-bearing plants evolved from spore-bearing ancestors.
Ferns (Polypodiopsida) are spore-bearing plants, which sets them apart from their seed-bearing cousins.
Photo Credit: Amy Prentice
Fern Resiliency
Ferns are resilient because they can photosynthesize in a wide range of light conditions, including very dark conditions. So if an asteroid hits the Earth and blots out the sun, ferns would fare better than most of their seed-bearing relatives.
“We think of them as these very sort of lacy, delicate, decorative plants,” Emily says of ferns. “But in fact, they can be quite tough.”
A question Emily is often asked about typical ferns is, where are the stems? Is every part growing out of the ground a leaf? The answer, in the case of most ferns, is that everything above ground is a leaf, or frond.
Temperate-region ferns have a rhizome that grows underground and is known as the stem. The rhizome persists year-round, while the leaves die off in winter.
Rhizomes grow a little further every year, spreading out among plant roots and mycorrhizal fungi. Ferns are resistant to fire because when the forest canopy burns, the rhizomes persist.
“If a wildfire comes through and burns all your leaves down, but your rhizome is buried six inches, a foot, five feet below ground, it’s not going to be bothered by that,” Emily says. “And it’s potentially going to be able to pop out new leaves really quickly after that fire goes through.”
I am involved with the Georgia Native Plant Society, which gets permission to visit future development sites to rescue native plants prior to land clearing. The plants are dug to be relocated someplace they will be safe from development. I love to dig ferns on these outings. When I expose the roots of a dormant fern, just below the soil surface, there’s a lot of green activity that looks like it’s lying in wait to come up at the appropriate time.
“Ferns in particular can be quite amenable to allowing themselves to be rescued, which is nice,” Emily says. “Sad that we have to do it, but nice that they cooperate.”
Dryopteris goldiana, which has the common names Goldie’s wood fern and giant wood fern.
Photo Courtesy of Dr. Emily Sessa
Ferns as Houseplants
In terms of houseplants, the most common fern is the Boston fern.
“They can get to be quite a handful,” Emily says. “They can get really big over time if you let them, but they’re actually quite amenable, I think, to being forgotten about. So they make good houseplants because they can tolerate being in the shade. They don’t need super bright conditions. And they do want to be watered, but if you forget to water them again, you might see them drying up and you might see them looking like they’re very unhappy. But in fact, what might be happening is that they’re sort of going dormant and they’re waiting for you to remember them and think about them.”
Pull off some dead leaves, give the plant some water, and you might be surprised by how willing they are to revive, she says.
Propagating Ferns
When planting ferns in your yard, Emily’s biggest piece of advice is to make sure you are growing native species.
“I don’t just say that because natives are a fad or anything,” Emily says. “It’s important to think about growing the ferns that belong in your area.”
Ferns that are adapted to your area will be happy to grow there. And Emily notes that some ferns may be sensitive to soil type and the amount of water they receive.
“If you go to the southwestern deserts of the U.S., you will find ferns there if you know what you’re looking for, and they’re really cool,” she says. “But I wouldn’t recommend planting them in like the Pacific Northwest or New York, where I live. They’re not going to be happy there. So you really want to make sure that you’re matching things to the local environment, and especially to the precipitation and humidity regimes that are common to your area.”
Your best bet is a native fern, which you may find at a nursery that specializes in native plants or even at a farmers market. The American Fern Society offers a spore exchange to purchase, for 50 cents plus the cost of a stamp, fern spores.
“You can grow ferns from spores, actually, and if anybody is interested in a challenge, that would be my number one recommendation for getting your own ferns,” Emily says.
If you find a fern in your area that you like, you can take a leaf or part of a leaf without digging up or destroying the plant to collect the spores. The time to take a leaf is when the sporangia — the spore-bearing structure — is near ready to pop open and release spores. This is usually midsummer and later, and the sporangia will be black-ish to brown-ish.
Early in the growing season, the sporangia will appear like little white or pale green dots on the underside of fronds. They darken as the season progresses.
“I have heard so many stories of people who are convinced that their fern in their house has an insect infestation or a fungal infestation, and they scrape all those things off,” Emily said.
The technical term for one of those dots is sorus — a cluster of sporangia.
“Typically what I’ll do is I’ll take that little leaflet and I put it in some kind of envelope, like a paper envelope, not a plastic bag,” Emily says. “And you want to put it somewhere that it can dry.”
She likes to tape the envelope to a lamp shade and let the heat from the light dry out the sporangia. A few days later, the sporangia will dehisce, or open, releasing the spores.
“Then you’ll have spores that you can try to plant, and see if you can grow some ferns. And there are some great resources on the web with instructions for how to do that,” she says.
The American Fern Society has a detailed resource on fern cultivation.
Ferns can be grown by collecting spores and encouraging them to germinate.
Ferns have two important stages in their life cycles: gametophyte, when they germinate from spores, and sporophyte, when they are in their leafy plant form.
Gametophytes are tiny — you could fit dozens on your fingernail — and each is a little independent plantlets, Emily says.
Fern spores can be placed on wet, sterilized potting soil in plastic takeout containers with a lid to retain humidity.
“The first thing that you’ll see will be these little gametophytes,” Emily says. “They’ll be these little green, leafy kind of heart-shaped plants. They’re sort of famous for being heart shaped, which is quite lovely. And those gametophytes, they are what we call the sexual stage of the life cycle because, just like us, plants make eggs and sperm. Not just like us, their sperm are a little bit different. Their eggs are a little bit different. But the basic sexual reproduction that we do in animals is the same in plants.”
The gametophytes make eggs and sperm, and if there is a successful fertilization event, that’s when big leafy sporophytes grow. The gametophytes will dry up, and the sporophytes will be what’s left.
“So if you pay really close attention, you can actually follow those different steps happening if you want to try to grow ferns from spores yourself,” Emily says.
Fern fronds emerge from the soil in spring.
Photo Credit: Amy Prentice
I hope you enjoyed my conversations with Dr. Emily Sessa all about ferns. If you haven’t listened yet, you can do so now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title.
Do you grow ferns and mosses in your garden? Let us know in the comments below.
Links & Resources
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Episode 226: The Magical World of Moss Gardening
joegardenerTV YouTube: How to Create a Moss Garden
joegardener Online Gardening Academy™: Popular courses on gardening fundamentals; managing pests, diseases & weeds; seed starting and more.
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joegardener Online Gardening Academy Master Seed Starting: Everything you need to know to start your own plants from seed — indoors and out.
joegardener Online Gardening Academy Beginning Gardener Fundamentals: Essential principles to know to create a thriving garden.
joegardener Online Gardening Academy Growing Epic Tomatoes: Learn how to grow epic tomatoes with Joe Lamp’l and Craig LeHoullier.
joegardener Online Gardening Academy Master Pests, Diseases & Weeds: Learn the proactive steps to take to manage pests, diseases and weeds for a more successful garden with a lot less frustration. Just $47 for lifetime access!
joegardener Online Gardening Academy Perfect Soil Recipe Master Class: Learn how to create the perfect soil environment for thriving plants.
“Ferns, Spikemosses, Clubmosses, and Quillworts of Eastern North America” by Dr. Emily Sessa
NYBG’s Plant People podcast with Dr. Emily Sessa
NYBG’s C.V. Starr Virtual Herbarium – Digitized specimen records and images are fully searchable
Proven Winners ColorChoice – Our podcast episode sponsor and Brand Partner of joegardener.com
Milorganite® – Our podcast episode sponsor and Brand Partner of joegardener.com
Disclosure: Some product links in this guide are affiliate links, which means we get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us, and compensation is not an influencing factor on their inclusion here. The selection of all items featured in this post and podcast was based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp’l has professional relationships with the following companies who may have products included in this post and podcast: Corona Tools, Milorganite, Soil3, Territorial Seed Company, Earth’s Ally, Proven Winners ColorChoice, Farmer’s Defense, Heirloom Roses and Dramm. These companies are either Brand Partners of joegardener.com and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.
