Thelypteris palustris aka Marsh Fern

Thelypteris palustris is a fern known as marsh fern. People also call it ground fern and marsh buckler fern. Its native range runs from central Canada south to Mexico. It is also native to Bermuda, Cuba, and Morocco. Its range includes temperate Eurasia too. The RHS lists it as native to Britain and Ireland. It grows in temperate zones, including open wetlands with full sun. It once had the name Dryopteris thelypteris. Another old name is Aspidium thelypteris.

This perennial fern loses its leaves each year. Its pale green fronds have a slim shape and stand upright. Each frond splits into many small parts. Some fronds bend or twist instead of standing straight. The RHS describes fronds around 1.6 feet [0.5 metres] tall. Chicago reports patches that reach 2.5 feet [0.76 metres]. The RHS gives a mature garden height of 1.6–3.3 feet [0.5–1 metre]. It lists the same range for the plant’s spread. Plants form clumps, then spread through stems below the soil. These stems, called rhizomes, can form dense patches of fronds over time.

Moist soil and part shade suit this fern well. Chicago also lists full sun as a good choice. Its account links the plant with wet or moist ground. The RHS accepts soil that drains well or poorly. It lists clay and loam, while Chicago favours sandy soil. Acid soil suits the plant. The RHS also accepts neutral soil. It calls for a site with shelter from wind. It lists sites that face north, east, or west. These choices help gardeners match the fern to local conditions.

The RHS rates its cold hardiness as H7. Chicago lists USDA zones 2–9. The RHS says it takes five to ten years to mature. Gardeners can split plants or grow new ones from spores. The RHS says this fern needs no pruning. It also reports few pest or disease problems. Neither source gives evidence that the plant is safe to eat. Neither gives evidence to judge whether it is toxic.

Its spread makes it useful as ground cover. It also suits beds, borders, and gardens with an informal style. The RHS suggests growing it beneath roses and shrubs. Its finely cut leaves add interest, rather than bright blooms. Chicago names it as the sole known host of the marsh fern moth. That moth’s caterpillars feed on the fern’s fronds.