Thursday, May 16, 2013

Outside Story: Fabulous Forest Ferns

fernsWe all see our forests for the trees, but the woods are alive with other plants. Among the most common are ferns, which don’t just get by in the deep shade of the forest – they flourish.

Now, you might be thinking, don’t all those ferns look alike? They form a lovely verdant backdrop to the forest, but they don’t have the showy flowers and distinctive leaves that make other plants so easy to identify. But ferns are surprisingly easy to tell apart. And once you know the names of a few species, they’ll pop out at you as you wander along forest paths.

Let’s start with an easy one, a species you can see any time of the year (as long as it’s not buried in snow): Christmas fern (Polystichum acrostichoides). Its name is telling, in more ways than one. First, it is one of the few ferns you will see alive on Christmas day. The leathery fronds of Christmas fern persist all winter, quietly photosynthesizing when sun pierces winter clouds. Also, peer closely at each of the leaflets growing along the frond. Hold one with the long axis pointing up, and you’ll notice a little “ear” that projects horizontally off the base of the leaflet where it joins the stem. Maybe the leaflet now reminds you of a Christmas stocking, with the foot angling sideways and the legging on the vertical? If you’re still in doubt, look at the stem of the frond. It will be covered with dense, shaggy, copper-colored scales. These scales help protect the fern from desiccating winter winds.

There are other forest ferns with golden, translucent scales, but their leaves are very different from those of Christmas fern – usually much lacier because each frond is divided into leaflets, which are further divided into separate leafules. These are the wood ferns – species in the genus Dryopteris. They are stout stalwarts of our forests, among the largest ferns of our flora. Although they most commonly inhabit the forest floor, sometimes you will spot one growing out of a rock face or crotch of a tree. To be absolutely sure you have a wood fern, turn over a frond and inspect it for small, kidney-shaped dots on the undersides of the leaflets. These are the organs that bear the spores that grow, eventually, into new ferns.

Wood ferns aren’t the only rock and tree dwellers. Our rock polypody species, in the genus Polypodium, commonly festoon acidic boulders, glacial erratics, and cliff faces, and will rarely grow directly on the ground. Like Christmas fern, their tough, deep-green fronds are hardy well into winter and can tolerate droughts and freezing conditions by curling up, only to spread out luxuriantly when conditions permit. Unlike Christmas fern, which bears masses of spores in specialized leaflets at the top of fronds, polypodies keep their spores in neat, round, rust-colored dots on the underside of their leaflets.

Now, for something completely different: maidenhair fern (Adiantum pedatum). The name maidenhair is evocative of the incredibly delicate nature of the fronds. Slender, black stalks bear half-moon umbrellas of blue-green, thin leaflets, each of which is less than an inch long. The edge of each leaflet is gently folded over to protect the tiny spores. Look for these ferns in forests with calcium-rich soils. Interestingly, a rare species of maidenhair fern in Vermont has adapted to the challenging soils of serpentine bedrock, the source of poisonous asbestos – proof positive that ferns, among the world’s oldest living plants, are evolutionarily versatile and resilient.

And finally, use all your senses to discover ferns. One of our most common species – to the point that some consider it “weedy” – is hay-scented fern (Dennstaedtia punctilobula – say that 10 times fast!). True to its name, it smells like new-mown hay in mid-summer. Its masses of frilly fronds wave in the breeze, distinctive for their light green color in July, mellowing to yellow-brown in fall. Use your sense of touch, too, to identify this fern: it is covered with tiny, white, glandular hairs that exude a sticky substance. That stickiness probably deters deer, which explains why hay-scented fern can form large colonies in forests otherwise depleted of tree seedlings by foraging Bambies. Hay-scented fern also bears some of the most unusual spore-bearing structures in our fern flora. Tiny goblets on the undersides of the leaves offer up minute, white, grapelike spores in late summer; you can glimpse these with a magnifying glass.

Perhaps this primer will pique your curiosity and you’ll learn a few more fern species. See the forest for the trees … and the ferns!

Elizabeth Farnsworth is Senior Research Ecologist with the New England Wild Flower Society, and co-author of the Peterson Field Guide to Ferns. The illustration for this column was drawn by Adelaide Tyrol. The Outside Story is assigned and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of New Hampshire Charitable Foundation: wellborn@nhcf.org.

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2 Responses

  1. Mike says:

    Great article, thanks! How is asbestos poisonous? I understand its carcinogenic properties in mammals (at least in lungs), but I never knew it was toxic to plants?

  2. Dr. Bill Kritzler says:

    I agree with Mike. Asbestos is silica which is essentially sand like. It only gives us problems when tiny particles of it get deep into our lungs and mess up the function of the aveoli. The real problem is that the body can’t get rid of the particles and the lungs are shot. I THINK that’s the story.