The giant sword fern or Blechnum attenuatum var. giganteum grows on stream banks in montane grassland and evergreen forests, often in the spray zone of waterfalls. This habitat is fragmented along the South African south and east coast areas, as well as to the north as far as Zambia, Malawi and Tanzania. Frost-free areas with strong indirect light such as dappled sunlight under trees and high humidity in moist places away from much wind that dries out the land, houses these plants.

Giant sword ferns grow tufts of fronds from their underground rhizomes.  They reach heights of around 1.8 m. The leaflets or pinnae have entire margins. They are broadly attached to the rachis, attenuate towards their tips (as the specific epithet indicates) and are smaller towards the frond base (www.forestferns.co.za; www.zimbabweflora.co.zw).