T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Nephrolepis cordifolia (Ladder fern)

Kingdom: Plantae
Division: Pteridophyta
Class: Filicinae
Order: Polypodiales
Family: Lomariopsidaceae
Genus: Nephrolepis
Species: N. cordifolia
Binomial name: Nephrolepis cordifolia
Synonyms: Aspidium cordifolium, Aspidium pendulum, Aspidium tuberosum, Aspidium volubile, Nephrodium pendulum, Nephrodium tuberosum, Nephrolepis radicans, Nephrolepis tuberose, Polypodium cordifolium.
Common names: Ladder fern, Erect sword fern,Tuber ladder fern, Chinese ladder fern, tuber sword fern, Boston fern, Fishbone Fern, Herringbone fern, Sword fern.

Nephrolepis cordifolia is a tropical or perhaps pantropical fern, Its classification in the NZ National Pest Plant Accord it is that it is banned from being sold, propagated or distributed. There is a similar native ladder fern, but it has no tubers and is rare and is found only in geothermal sites and on Raoul Island.
Nephrolepis cordifoli is a terrestrial or epiphytic fern that grows to one metre in height, with rhizomes and producing many long runners. Tuber ladder ferns have round, 1-3cm hairy potato-like tubers. This is the only fern with tubers. Leaves: fronds are 40-100 x 5-8cm erect and arching when long with serrated leaflets Tuber ladder ferns spread by spores, runners and tubers. Dense, long-lived patches are formed, often spreading to cover large areas. It grows in damp or dry, on ground or trees, in the open or shady spots. It can grow in most soil types, and in hot to mid-cool temperatures. It invades disturbed bush and shrubland, fern land, tussock land, coastal forest and stream sides by crowding out groundcovers, shrubs and other ferns. It can contribute to streamside erosion. Runners and tubers quickly spread from dumped vegetation and soil, occasionally through flooding. Runners and tubers will both resprout if not disposed of carefully.

This is the only fern with tubers. 

The top side of fertile frond

The underside of a fertile frond
The top surface of a sterile frond.

The underside of a sterile frond.
Growing tip of a frond.
Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0/