Identifying the Native Ferns of Maine

Compared to wildflowers, ferns can be tricky plants to identify since many fern species have very similar characteristics and their differences can be subtle. However, with a careful eye and a good plant identification book, even novice naturalists and beginning gardeners can identify fern species correctly. And, of course, if you want to use ferns in your native garden landscape, the first step is being able to identify the plants you’re working with!

Native Gardens of Blue Hill offers many interesting and useful workshops throughout the year, and I’ve had the privilege of attending a few over the last few months. Most recently, I stopped by the Fern ID workshop led by NGBH Co-founder Cathy Rees. I learned so much, I wanted to share the basics of fern ID with you!

Identifying Ferns: What to Look For

From a distance, ferns may look similar, but each fern species has its own unique characteristics that can be used for identification purposes. Websites like Go Botany can help you identify particular fern types, or you can invest in a good fern identification book with a dichotomous key. You may also want to pick up a 10X jeweler’s loupe to help you see all of the fine details on the fern plants you’re working with. If you’re new to using a dichotomous key for plants, think of it as essentially a “decision tree” made of a series of two basic questions or statements about plant characteristics. By selecting the statements that best describe the plant you have in your garden, you can narrow down potential fern species until you arrive at a name for the type of fern you have!

As Cathy described in the fern ID workshop, dichotomous keys for ferns focus on particular elements of fern plants. For instance, a dichotomous key may ask you about the shape of a fern blade or how the sori (the clusters of sporangia where ferns store their spores) are arranged on a fern leaf. If you’re trying to identify a fern with a dichotomous key, some of the most important features to pay attention to include:

General growth form. Fern plants can grow with their fronds in clusters, or the fronds may be scattered along the plant’s underground rhizome. Pay attention to how tightly or loosely fern plants arrange themselves as they grow, as this can help you with fern identification!
General leaf shape. Fern leaf blades come in a range of shapes, but most commonly, you’ll find that fern leaves are either broad at the base, tapered to the base or semi-tapered. Noting the general silhouette of fern blades can help you narrow down particular fern species using a dichotomous key.
Leaf stalk details. A “stalk” runs up the center of the fern frond; however, unlike with flowering

plant leaves, a fern stalk is referred to as a “stipe” (the part below the leaf blade) or a “rachis” (the part within the fern blade). Different fern species can have a rachis and stipe that’s smooth, hairy, woolly, glandular (covered in small nubs) or scaly and this, too, can be useful for identification!* * Note: A loupe can help you see these features!

Leaf division. Fern blades can have an undivided shape, but most fern blades are divided into smaller sections (known as pinnae and pinnules), which give the fern fronds their characteristic, feathery outlines. How many times a fern blade is divided can be useful for ID purposes, and you can find undivided ferns (smooth shape without pinnae), once-divided ferns (blade is divided into pinnae – like a leaflet on a compound leaf), twice-divided ferns (blade has pinnae that are further divided into pinnules) and even thrice-divided ferns (where the pinnules are also divided)!
Arrangement of sori. Sori are where ferns develop their spores, which the plant uses for reproduction. Sori are generally found on the undersides of fern leaves. They can be arranged along the leaf’s margins or central vein, or the sori can be scattered randomly about the leaf’s surface.* Sometimes they are on a special frond, or on some of the pinnae that look different from the non-reproductive pinnae.

As you can see, there’s more to fern identification than meets the eye, but if you work your way through a dichotomous key, you can pinpoint the exact fern species you’re working with.

Are the fern fronds clustered? Scattered? Is the fern’s stipe hairy or smooth?

Simple questions like this will help you arrive at an exact plant identification. Once you ID the fern type you have, you can research the plant’s specific care requirements to ensure it will thrive in your garden!

Native Ferns of Maine

There are a number of different native ferns in Maine, but some of the most common ferns you’ll likely encounter on a nature walk can be found below. Many native Maine ferns can also be purchased at local plant nurseries or native plant sales if you’d like to add these stunning plants to your landscape design!

Cinnamon fern. Known for its prominent, cinnamon-colored fertile fronds, cinnamon ferns can be found growing along streambanks, but this clump-forming fern is also a good candidate for shade gardens with moist soil.
Interrupted fern. A very adaptable, clumping fern species, interrupted ferns prefer dappled light, but they can potentially tolerate even full sun as long as they receive adequate watering.
Royal fern. A stately plant, royal ferns can stretch up to 6’ tall and they make excellent backdrop plants in shade gardens; however, these ferns need plenty of water to thrive.
Wood fern. These ferns may have delicate looking fronds, but they’re surprisingly tough and they can grow in a range of conditions. A solid choice for a low maintenance groundcover, wood ferns are clumpers and spread by spores when provided with the right balance of moisture, nutrients and light.
Hay-scented fern. Named for its sweet and delicate aroma, which is reminiscent of the fragrance of freshly cut hay, hay-scented ferns are a fast-growing species that spread rapidly as they expand their colonies.
Sensitive fern. A top choice for dappled shade, it is a spreader and prefers moist soil. Sensitive fern is a deciduous fern species that drops its leaves in winter. This characteristic is how the plant got its name!

Maidenhair fern (adiantum pedantum), courtesy of NGBH

How to use ferns in the landscape

Ferns are relatively easygoing plants as long as you provide them with the proper garden conditions. Most ferns are ideal for shade gardens, and they prefer full to partial shade, although there are a few fern species that can handle direct light. That said, ferns grown in sun usually need to be watered often.

Beyond shade, most ferns also prefer slightly acidic soil, which is great news for Maine gardeners as Maine soils tend to be on the acidic side. Even better, since most ferns love lots of moisture, many fern species can be kept in rain gardens or around water features for extra interest and color.

Depending on the ferns you’re working with, you can either grow different fern species together in a dedicated fern bed, or you can mix ferns in with other flowering native plants. Some native plants that thrive in the moist soil and shady conditions that ferns prefer include foamflower, blue lobelia and bunchberry, although you can certainly try ferns with other ornamentals for even more variety!