Topic: sweet fern
Is part of topic Common New Zealand ferns
Recognition: medium-sized ground fern. The frond is pale green, generally thin (thicker when growing near the coast), has netted veins, and is distinctively fractal (i.e., the bigger segments are made up of smaller but similarly-shaped segments). The sporangia (which produce spores) are aggregated into sori along the margins of the undersides of the frond segments, and are protected by the margin being inrolled.
Distribution/ecology: only found in New Zealand. In lowland forest throughout the North Island, but limited to the north and west coasts of the South Island.
Relationships: often occurs with the shaking brake (Pteris tremula). The shaking brake, which is also indigenous to Australia and Fiji, differs in its fronds being less fractal-like and in having more linear segments and free (not netted) veins. Compared to sweet fern, shaking brake is less likely to be in dense forest and more likely to be in open, disturbed areas. Two other species of Pteris are also indigenous to New Zealand, but they are much less common: coastal brake (Pteris comans) and Pteris saxatilis (both northern North Island, and mainly coastal). Several exotic Pteris have become weedy in New Zealand.
Pteris is part of the Pteridaceae fern family, whose other indigenous New Zealand representatives are Adiantum, Anogramma, Cheilanthes, and Pellaea.
Some members of the Dennstaedtiaceae similarly have linear sori protected by the inrolled frond margin and might be confused with Pteris. However, these Dennstaedtiaceae can be distinguished by other features: bracken (rarauhe, Pteridium esculentum) has a tougher, thicker frond; water fern (mätä, Histiopteris incisa) has a bigger, lighter-coloured frond.