Osmundastrum cinnamomeum aka Cinnamon Fern

Osmundastrum cinnamomeum is known as cinnamon fern. It belongs to Osmundaceae, the royal-fern family. It is native to eastern North America and tropical America. Its range also includes eastern Asia. It grows in swamps, damp woods, and wet ground near streams. It also grows on shaded rock ledges and bluffs. This fern lives a long time and grows in clumps. These grow from short rhizomes, stems that spread sideways. It sheds its leaves in autumn. In warm winters, though, the leaves may stay.

Most garden clumps stand 2–3 feet [0.61–0.91 metres] tall. Reports give widths of 2–4 feet [0.61–1.22 metres]. With steady moisture, heights can reach 5–6 feet [1.52–1.83 metres]. Curled young leaves, called fiddleheads, rise from the base in spring. They open into yellow-green fronds, the fern's leaves. These stand upright at first, then arch. They can reach 2–4 feet [0.61–1.22 metres] long. Their narrow leaflets have pointed tips and deep cuts. These give the leaves a fine texture. Rust-coloured hairs grow under the base of each leaflet. The green fronds last through summer, then turn yellow in autumn.

Separate fertile fronds grow among the green leaves in early spring. These bear spores and are stiff and narrow. They soon turn cinnamon brown. Their spore cases give the fern its common name. These fertile fronds die back by midsummer. The fern has no flowers or fruit. It spreads by spores instead. Songbirds use its stem hairs to line their nests. Kentucky warblers also nest in its clumps. The clumps provide ground cover.

Give it partial to full shade and moist to wet soil. It prefers rich, acidic soil with plenty of humus. It can cope with poorer soil too. Dry ground may make it go dormant. It takes time to settle in, then grows strongly. Missouri Botanical Garden lists USDA hardiness zones 3–9. Use it by ponds, streams, or water gardens. It also suits bogs, shaded borders, and plantings in woods. Its leaves add texture in summer and colour in autumn. Sources report no major problems with pests or disease. Deer seldom harm it, and it resists rabbits too.

Reports list young, unopened fronds and early spring buds as food. Useful Tropical Plants gives no reports of poisoning for this species. This lack of reports does not mean it is safe to eat. Its warning about harmful compounds applies to ferns more broadly. Reports of folk remedies describe roots used for joint pain and other ailments. These records show past uses, not proof that the treatments work. The roots also supply fibre for orchid potting mixes.