Asplenium marinum
sea spleenwort
Atlantic coasts of Europe and Macaronesia
Overview
Asplenium marinum is a small evergreen fern of sea cliffs and coastal caves, forming tufts of leathery fronds 6-12 inches (15-30 cm) long, occasionally longer in sheltered crevices. The fronds are once-pinnate, with 10-20 pairs of rounded to oblong leaflets along a glossy reddish-brown to purplish midrib, and arch outward from a short creeping rhizome wedged into rock. The leaflet surface is thick and waxy, an adaptation to salt spray and drying wind. Spores form in linear clusters (sori) on the undersides of the leaflets, ripening through summer and autumn, and the fern reproduces by these rather than by flowers or seeds. It grows in the splash zone of the sea, in crevices, cave mouths, and old harbor walls where its roots stay cool and the air is salt-laden and humid. The fern is frost-tender and confined to mild, oceanic coasts, dying back where hard freezes reach. Its strict need for a humid, frost-free, maritime setting makes it hard to grow inland or in cold gardens. The evergreen fronds stay green through winter in its natural range.
Native Range
Asplenium marinum is native to the Atlantic coasts of western and southern Europe, from Norway to the Mediterranean, and the islands of Macaronesia. It grows almost exclusively within reach of salt spray on sea cliffs, in caves, and on coastal rocks and walls.Suggested Uses
Grown in shaded rock crevices, walls, troughs, and cool greenhouses in mild, humid coastal gardens. It suits maritime and naturalistic plantings where frost is rare. Its tolerance of salt spray fits it for seaside walls and rock pockets.How to Identify
Appearance
Size & Dimensions
Height6" - 1'
Width/Spread8" - 1'4"
Bloom Information
This fern does not flower. Spores ripen in linear sori on the frond undersides through summer and autumn and are shed to start new plants, completing reproduction without seeds or flowers.
Detailed Descriptions
Foliage Description
Dark glossy green with reddish-brown midribGrowing Conditions
Sun Requirements
Tolerates up to 4 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 light to deep shade in cool, humid, frost-free conditions, rooted in gritty, sharply drained crevices or rock and wall pockets near the sea. It is frost-tender, hardy only to about USDA zone 9, and is damaged or killed by hard freezes. It tolerates salt spray that few other ferns withstand but needs constant atmospheric humidity and cannot dry out at the root. In gardens it is grown in shaded crevice plantings, troughs, or cool greenhouses in mild coastal areas. Slugs may graze young fronds, and dry air browns the foliage.Pruning
Old, browned, or frost-damaged fronds are cut away at the base in spring as new croziers unfurl. No other pruning is needed. The fern is otherwise left undisturbed in its crevice.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
early spring
Container Growing
✓ Suitable for container growing
Minimum container size: 2 gallons