The giant sword fern or Blechnum attenuatum grows tufts of fronds from underground rhizomes. The plants reach heights 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.

Giant sword ferns are found along stream banks in montane grassland and evergreen forests, often in the spray zones of waterfalls. This habitat is fragmented and limited along the South African south and east coasts, the Mpumalanga and Limpopo Lowveld, 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 are suitable to these plants. The species is not considered to be threatened in its habitat early in the twenty first century (www.forestferns.co.za; www.zimbabweflora.co.zw; http://redlist.sanbi.org).