Etymology Aculeatum means prickly.

Description Rhizome: erect, branching, stout.
Frond: 60 cm high by 14 cm wide, evergreen, remaining green through the following summer, monomorphic, blade/stipe ratio: 5:1.
Stipe: grooved, mixed large and small reddish-brown scales, smaller and narrower upwards to hair-like at the top of the rachis, vascular bundles: 4 or more, in an arc.
Blade: 2-pinnate, juveniles less, more divided closer to the rachis and closer to the base, lanceolate, glossy, leathery, dark green, linear to lanceolate scales on rachis and costa, lamina glabrous above, a few sparse hairs or scales below.
Pinnae: 25 to 40 pair, subopposite, lowest pinnae half the length of the middle ones, pinnae generally curving upward; pinnules adnate to the pinnae, the first pinnule on the upper side generally larger than the others; all pinnules have an outward-pointing spiny-tipped lobe at the base, curved towards the pinna apex; costae grooved above, not continuous with rachis; margins very spiny; veins free, forked, anadromic.
Sori: round, in 1 row on each side of the costa between midrib and margin on the upper half of the blade, indusium: peltate, shriveling upwards like an inverted umbrella, but persistent, central, sporangia: dark brown or black, maturity: midsummer to mid-winter.

Culture Habitat: uplands, rocky outcrops, on limestone. Distribution: Europe, northern Africa and perhaps eastward to the Himalayas, Japan, Taiwan. Hardy to -30°C, USDA Zone 4.

Distinctive Characteristics Similar in many respects to P. braunii, but the pinnae at the base are half the length of the middle (not tiny). This is also a smaller plant with fewer fronds, a glossier lamina.

Synonyms
Polypodium aculeatum L.
Polystichum lobatum (Huds.) C. Presl
Aetopteron aculeatum House
Aspidium aculeatum (L.) Swartz
Aspidium aculeatum ssp. lobatum (Hudson) Niessl
Aspidium munitum Sadl.
Dryopteris aculeata O. Ktze.
Dryopteris setifera ssp. lobata (Hudson) Maire
Hypopeltis aculeata Tod.
Tectaria aculeata Lag., Garcia & Clem.