Polystichum aculeatum (Hard Shield Fern) is an evergreen fern native to Europe. It is most abundant in upland regions of the British Isles and western France, where it benefits from the combination of mild winters and moist summers, but also occurs more locally across most of Europe except northern Scandinavia, northern Russia; in the Mediterranean region it is confined to high altitudes. It grows on steep slopes in woodlands.
The glossy dark green fronds are 30–90 cm long, usually drooping downslope, with typically 3-8 fronds on a mature plant. The fronds are stiff and hard-textured, bipinnate (single-pinnate on small, young plants), with the pinnae opposite on the stalk. Each pinna is 3–11 cm long, with a large upward-pointing pinnule at the base, and the other pinnules decreasing in size toward the pinna tip; the pinnules have bristly tips. Individual fronds live for 1.5-2.5 years and remain attached to the rhizome after withering. The round sori occupy two rows on either side of the midrib of each pinnule and are covered by a centrally-attached, umbrella-like indusium with fringed edges. They produce light yellow spores.
It is occasionally grown as an ornamental plant in gardens.
- Hackney, P. Ed. 1992. Stewart & Corry's Flora of the North-east of Ireland. Institute of Irish Studies and The Queen's University of Belfast.
- Welsh Ferns; Hutchinson & Thomas; Seventh edition; 1996
- Flora Europaea: Polystichum aculeatum
- Swan, G. A. (1993). Flora of Northumberland. Natural History Society of Northumbria.
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