hard shield fern
Polystichum aculeatum, the hard shield-fern, is an evergreen fern native to Europe. It is most abundant in upland regions of the Atlantic Archipelago 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. it is sometimes considered an indicator of the presence of ancient 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.
Ireland. Counties:Down, Antrim and Derry. Throughout the British Isles and Europe except for the northern countries. It is found in mountain limestone screes in the Jura and the alps, and on alpine and subalpine limestone cliffs.
- BSBI List 2007 (xls). Botanical Society of Britain and Ireland. Archived from the original (xls) on 2015-06-26. Retrieved 2014-10-17.
- Rose, Francis. "Indicators of ancient woodland: The use of vascular plants in evaluating ancient woods for nature conservation" (PDF).
- Harrison, Lorraine (2012). RHS Latin for Gardeners. United Kingdom: Mitchell Beazley. ISBN 978-1845337315.
- "RHS Plantfinder - Polystichum achuleatum". Retrieved 12 May 2018.
- "AGM Plants - Ornamental" (PDF). Royal Horticultural Society. July 2017. p. 81. Retrieved 12 May 2018.
- 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
- "INPN: Habitat of Polystichum aculeatum". INPN Inventaire National du Patrimoine Naturel. Retrieved 2018-05-21.
- Bensettiti, F., & Muséum national d'histoire naturelle (Paris). 2004. Habitats côtiers. la Documentation française.
- Flora Europaea: Polystichum aculeatum
- Swan, G. A. (1993). Flora of Northumberland. Natural History Society of Northumbria.
|Wikimedia Commons has media related to Polystichum aculeatum.|