Consult a fern identification guidebook or database. Guidebooks are available at the public library, online or at bookstores. Several websites provide interactive databases with photos of many of the different species of fern.
Examine the underside of the fern leaf. Ferns propagate by rhizomes that spread under the soil and by spores that develop on the underside of the leaf. Spores resemble dots on the leaf. Spore spots are called sori. The spots may be black, brown, green or yellow and vary in size and pattern depending on the species of the fern.
Examine the size of the fern. Rattlesnake fern (Botrychium virginianum) is one of 12 species of grape fern that grow in the cooler regions of the United States, Canada and Europe. Rattlesnake fern is the most common of the grape ferns. Growing from 12 to 18 inches tall, the plant can be found in shaded, moist forests with nutrient-rich soil. The plant has a single leaf, paired with a single frond. Coin spot tree fern (Cyathea cooperi) is a large, evergreen tree fern that grows up 40 feet tall.
Look at the color of the stalk or stem. Fragile Fern (Cystopteris fragilis) also known as brittle fern, grows from 12 to 18 inches tall grows only in rich woodlands. Found mainly in rock outcroppings, this fern's leaves have a stalk or stripe that is a dark brown.