Asplenium ruta-muraria
wall-rue
Europe, temperate Asia, North America
Overview
Asplenium ruta-muraria is a small, tufted evergreen fern that grows in the crevices of limestone rocks, mortared walls, and masonry across Europe, Asia, and North America. The fronds are 1-5 inches (2.5-12 cm) long, leathery, and irregularly divided into a few small, wedge- to diamond-shaped leaflets with toothed tips, giving them a look closer to a small flowering herb than a typical fern. The foliage is dull blue-green and held in dense tufts from a short, branching rhizome wedged into cracks. Narrow lines of spore clusters form on the leaflet undersides and merge as they ripen, shedding spores from summer into autumn. The fern roots in tiny pockets of lime-rich grit and mortar, drawing moisture from rain and the surrounding stone, and survives long dry spells by curling its leathery fronds. It is slow-growing and long-lived, forming small colonies that persist for many years on old walls and cliffs. It tolerates exposure, cold, and drought but needs the alkaline conditions of limestone or mortar and declines on acidic substrates. Loss of old lime-mortared walls has reduced its habitat in some regions.
Native Range
Native across Europe, temperate Asia, and parts of North America, where it is most frequent in limestone districts. It grows in rock crevices, on cliffs, and in the mortar of old walls, bridges, and buildings.Suggested Uses
Grown in crevice gardens, on dry stone and mortared walls, in tufa and limestone rockwork, and in alpine troughs. It suits shaded, lime-rich nooks where larger ferns would not root.How to Identify
Appearance
Size & Dimensions
Height1" - 5"
Width/Spread2" - 5"
Reaches mature size in approximately 5 years
Bloom Information
As a fern, this species reproduces by spores rather than flowers. Narrow spore clusters form on the leaflet undersides and merge as they mature, releasing spores from summer into autumn. Wind carries the spores to other lime-rich crevices.
Detailed Descriptions
Foliage Description
Blue-greenGrowing Conditions
Sun Requirements
Requires 2-5 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Grows in part shade to dappled light in gritty, sharply drained, lime-rich soil or directly in wall and rock crevices. It needs alkaline conditions and declines in acidic or rich, wet soil. Hardy in USDA zones 4-8, it keeps its fronds through winter and tolerates cold and exposure. It is slow to establish and resents disturbance once rooted in a crevice. Watering is light, with rain usually enough on walls and rockwork. Crushed limestone or mortar mixed into the planting pocket supplies the lime it requires.Pruning
No pruning is needed. Dead or weathered fronds can be picked off in spring as new ones unfurl. The small tufts are otherwise left undisturbed to spread slowly in their crevice.Container Growing
✓ Suitable for container growing
Minimum container size: 1 gallons