Growing interrupted fern plants, Osmunda claytoniana, is easy. Native to the Midwest and Northeast, these shade-tolerant plants grow in woodland sites. Gardeners add them to plantings of Solomon’s seal and hostas, or use the ferns to create a shaded border. Interrupted ferns even do well as erosion control plants on shaded slopes.
I. Appearance and Characteristics
Claytosmunda is a genus of fern. It has only one extant species, Claytosmunda claytoniana (synonym Osmunda claytoniana), the interrupted fern, native to Eastern Asia, Eastern United States, and Eastern Canada.
The specific epithet is named after the English-born Virginian botanist John Clayton. “Interrupted” describes the gap in the middle of the blade left by the fertile portions after they wither and eventually fall off.
The plant is known from fossils to have grown in Europe, showing a previous circumboreal distribution. Fragmentary foliage resembling Claytosmunda has been found in the fossil record as far back as the Triassic.
The species was first described by Carl Linnaeus in 1753, as Osmunda claytoniana. In 2005, it was recognized as being somewhat different from other species in the genus by being placed in a separate subgenus, Osmunda subgenus Claytosmunda. In 2016, the subgenus was raised to a new genus, Claytosmunda, as part of the Pteridophyte Phylogeny Group classification (PPG I).
The change of genus is recognized in some taxonomic databases. Others place the species in the genus Osmundastrum. The oldest known species of Claytosmunda is C. beardmorensis, from the Middle Triassic of Antarctica. Claytosmunda when considering fossils is paraphyletic, as some of the fossils are likely to be more closely related to modern Osmunda and Plenasium than they are to the modern C. claytoniana.
Claytosmunda claytoniana fronds are bipinnate, 40–100 cm (16–39 in) tall and 20–30 cm (8–12 in) broad, the blade formed of alternate segments forming an arching blade tightening to a pointed end. The lower end is also slightly thinner than the rest of the frond because the first segments are shorter. Three to seven short, cinnamon-colored fertile segments are inserted in the middle of the length, giving the plant its name.
In their absence, the plant in all its stages appears similar to Osmundastrum cinnamomeum (cinnamon fern). The base of the segments distinguishes the two species: where O. cinnamomeum has typical felt-like hairs, the few hairs present on C. claytoniana are extremely short, usually requiring a magnifying glass to see well.
Like other species in the family Osmundaceae, it grows a very large rhizome, with persistent stipe bases from previous years. It forms small, dense colonies, spreading locally through its rhizome, and often forming fairy rings.

II. How to Grow and Care
Interrupted fern thrives in consistently moist, well-draining soil and shaded to partially shaded areas, mimicking its natural forest habitat. It requires minimal maintenance, making it relatively easy to care for. Special attention should be paid to water and light conditions, avoiding overly dry soil and direct sunlight which can cause stress to interrupted fern.
Sunlight
Interrupted fern’s optimal light environment is one of full shade, where the intensity of direct sunlight is significantly subdued. This preference for lower light intensity does not preclude the plant from surviving in areas with partial shade, though such deviations can impact interrupted fern’s vitality, potentially resulting in less robust fronds and slower growth rates. Interrupted fern exhibits an innate resilience to light variance and may adapt by adjusting leaf orientation to optimize light absorption.
When cultivated outdoors, it thrives best under the canopy of taller vegetation, and it’s not commonly grown indoors. Locations that emulate its natural woodland habitat will support interrupted fern’s health and development most effectively.
Watering
Thriving in its native humid woodland environments, interrupted fern has adapted to regular moisture availability and exhibits a preference for consistent soil hydration. It is moderately drought-tolerant but flourishes when the soil remains evenly moist without becoming waterlogged. Watering every week will maintain its optimal hydration balance. Typically grown outdoors due to its affinity for a natural ecosystem, interrupted fern demonstrates a robust growth cycle that is highly influenced by the seasonal rainfall patterns of its habitat.
Soil
Interrupted fern is best grown in rich, consistently moist, acidic, well-drained soils. Do not allow the soil to dry out.
Fertilizing
For optimal growth, interrupted fern benefits from fertilization with balanced nutrition fertilizers. Apply a diluted solution of a balanced, water-soluble fertilizer monthly during the growing season (spring to early fall). Approximately 1/4 to 1/2 recommended strength should suffice, avoiding over-fertilization. Fertilization encourages robust frond development and overall vigor of interrupted fern. In winter, reduce to bi-monthly or cease as growth slows. Always water interrupted fern prior to application to protect roots from fertilizer burn. Gradually adjust the schedule based on plant response and environmental factors.
Propagation
As a distinctive perennial, interrupted fern showcases characteristic fronds with fertile leaflets ‘interrupted’ by non-fertile ones. Optimal propagation begins with sowing spores, preferably in a sterile medium to prevent contamination. A humid, stable environment supports spore germination and initial growth. Once sporelings develop, careful transplantation encourages robust root systems. Consistent moisture and indirect sunlight nurture juvenile interrupted fern to maturity for a vibrant display.
Transplanting
Best to relocate interrupted fern during the brisk vitality of early to mid-spring, optimal for root establishment. Seek shady spots with moist soil. Gentle handling of roots and fronds ensures a successful transition.
III. Uses and Benefits
- Ornamental uses
This plant is a great choice for shady beds, borders, underplanting of roses and shrubs, cottage gardens, woodlands, bog gardens, or along streams, ponds, or water gardens. Combines beautifully with Azaleas, Astilbes, Hostas, or Primulas.
- Medicinal uses
The Iroquois used the plant as treatment for blood disorders and venereal diseases.