Austroblechnum penna-marina, synonym Blechnum penna-marina, known as Antarctic hard-fern, Little Hard Fern, Alpine Hard Fern, alpine water fern and pinque (Chilean Spanish), is a species of fern in the family Blechnaceae. It is a widely distributed fern species in the southern hemisphere, with a natural range including New Zealand, Australia, and South America.

It has wiry rhizomes and exhibits strong dimorphism in its fronds. The sterile fronds are prostrate or semi-erect, growing up to 400 mm in length, while the fertile fronds are longer and held erect. The sterile fronds have a yellow-brown stem, while the fertile fronds have a purplish-black stipe. Both types of fronds have pinnatisect laminae with free veins. The sterile fronds have 12–44 pairs of triangular or oblong pinnae, while the fertile fronds have 10–36 pairs of linear to narrowly oblong pinnae, which are replaced by tiny sterile flanges at the base.

This fern prefers coastal to alpine environments, including open forests, grasslands, subalpine scrub, alpine herb fields, creek beds, river terraces, and rocky herb fields. It can be found from sea level up to 1900 meters above sea level. The preferred temperature range for its productivity is 6 to 11 degrees Celsius. It faces predation from endemic alpine grasshoppers such as Brachaspis nivalis, Paprides nitidus, and Sigaus australis.

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