Parablechnum cordatum (synonyms Blechnum cordatum, Blechnum chilense), the Chilean hard fern or costilla de vaca (Chilean Spanish for "cow's rib"), is a fern of the family Blechnaceae, native to Chile. It is also found in neighboring areas of Argentina and the Juan Fernández Islands.

It grows to 0.9–1.8 m (2 ft 11 in – 5 ft 11 in), often developing a trunk-like appearance over time. The fertile fronds are more erect, with narrower pinnae, than the infertile ones.

This plant has gained the Royal Horticultural Society's Award of Garden Merit.

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