Blechnum capense is a tufted fern with fronds of up to 1,3 m in length growing from a thick rhizome covered in brown scales. Branching of the rhizomes may result in crowded clumps of the plant. A dense crown of fronds may be formed on a flourishing, mature plant. The upper surfaces are fresh green, below more whitish. The leaflets growing from the central black midrib have scalloped or toothed margins.
Only some fronds are fertile; the fertile ones have leaflets spaced further apart and narrow with sori along their lengths. The sori are covered by a continuous indusium, a membrane that protects the spores.
This fern is variable, occurring from the Western Cape to tropical Africa, mainly on shaded stream-banks (Bean and Johns, 2005).