Fronds uniform or dimorphic with the fertile fronds usually much narrower than the sterile, vernation circinate; lamina simple, 1-pinnatifid or 1-pinnate, usually leathery.
Sori linear parallel with the midvein, one on each side of, and continuous along the midvein of the frond or segment or one or more rows of linear, discontinuous sori along the midvein and on the frond (the old Doodia); indusium linear, membranous, opening towards the midvein.
A proposal to split Blechnum into 15 genera by Gaspar et al. (2016) was adopted by the global Pteridophyte Phylogeny Group. This split maintains the genus Doodia, which rendered Blechnum sens. lat. paraphyletic. NSW has yet to apply the proposed segregation of Blechnum to the collection. See Gasper AL de, Almeida TE, Dittrich VAO, Smith AR, Salino A (2017) Molecular Phylogeny of the fern family Blechnaceae (Polypodiales) with a revised genus level treatment. Cladistics 33: 429–446. https://doi.org/10.1111/cla.12173, and Gasper AL de, Dittrich VAO, Smith AR, Salino A (2016) A classification for Blechnaceae (Polypodiales; Polypodiopsida); new genera, resurrected names and combinations, Phytotaxa 275(3): 191–227. https://doi.org/10.11646/phytotaxa.275.3.1
| | Key to the species | |
| 1 | Sterile and fertile fronds more or less similar, though the pinnae or segments on fertile fronds are usually somewhat narrower than the on sterile fronds. | 2 |
| Sterile and fertile fronds rather different, fertile pinnae less than half as broad as the sterile ones. | 5 |
| 2 | Sterile pinnae adnate, attached to the rachis by broad bases. | Blechnum cartilagineum |
| Sterile pinnae distinctly stalked, at least in the lower third of lamina.
Back to 1 | 3 |
| 3 | Fronds erect from an erect rhizome, shiny green; margins of pinnae ± equally finely toothed for their entire length. | Telmatoblechnum indicum |
| Fronds usually pendent from a creeping rhizome; margins of pinnae becoming more coarsely toothed towards their tips.
Back to 2 | 4 |
| 4 | Fertile pinnae more than half as broad as the sterile pinnae. | Blechnum gregsonii |
| Fertile pinnae less than half as broad as the sterile pinnae.
Back to 3 | Blechnum ambiguum |
| 5 | Fronds simple or 1-pinnatifid (often mixed on the one plant), with few pairs of widely alternate pinnae that are never divided all the way to the rachis. | Blechnum patersonii |
| Fronds 1-pinnatisect or 1-pinnate, with many pairs of closely spaced alternate pinnae that are either divided all the way to the rachis, or very nearly so.
Back to 1 | 6 |
| 6 | Pinnae not stalked, lamina fused with rachis on one (the side toward the frond apex) or both sides of the costa throughout the sterile lamina. | 7 |
| Pinnae stalked, lamina not fused with rachis on either side, at least in the lower half of the sterile lamina.
Back to 5 | 11 |
| 7 | Sterile pinnae in basal half of frond fused and decurrent down the rachis on both sides of the costa. Stipe with or without scales | 8 |
| Sterile pinnae in basal half of frond with lamina free and auriculate on the basal side of the costa, fused and decurrent down the rachis on the apical side of the costa. Stipe with long thin scales
Back to 6 | Blechnum fullagarii |
| 8 | Sterile pinnae free from one another for most of the length of the frond. | Blechnum fluviatile |
| Sterile pinnae with decurrent bases.
Back to 7 | 9 |
| 9 | Apex of sterile segments rounded to obtuse, generally rather blunt. | Blechnum penna-marina |
| Apex of sterile segments acute to acuminate, generally rather pointed and sharp.
Back to 8 | 10 |
| 10 | Pinnae margins on sterile fronds entire, fronds rigid, 35–120 mm long in the middle of the frond; rachis dark and glossy. | 14 |
| Pinnae margins on sterile fronds crenate, fronds flaccid, 10–25 mm long in the middle of the frond; rachis not glossy, usually straw-coloured.
Back to 9 | Blechnum chambersii |
| 11 | Basal pinnae only slightly smaller than the middle pinnae, more than half the length of the middle pinnae. | 12 |
| Basal pinnae much reduced in size, much less than half the length of the middle pinnae; sometimes only the basal pinna pair only are reduced and these may be quite small and displaced some distance down what appears to be the stipe.
Back to 6 | 13 |
| 12 | Rhizome scales dark brown to black, with a pale border and finely toothed margin; fertile pinnae 2–3 mm wide. | Blechnum wattsii |
| Rhizome scales brown to reddish brown; fertile pinnae 3–10 mm wide.
Back to 11 | Blechnum ambiguum |
| 13 | Lowermost sterile pinnae 5–15 mm long, circular. | Blechnum minus |
| Lowermost sterile pinnae mostly over 20 mm long, occasionally only 15 mm long, ovate to lanceolate. Sterile pinnae often auriculate at the base.
Back to 11 | 16 |
| 14 | Fronds bent at a sharp angle at the junction between the stipe and the rhacis. Sterile and fertile fronds triangular-ovate in outline. Pinnae 15–18 mm wide at their attachment with the rhacis | Blechnum geniculatum |
| Fronds not bend at the junction between the stipe and rhacis. Sterile and fertile fronds lanceolate in outline. Pinnae 8–9 mm wide at their attachment with the rhacis
Back to 10 | 15 |
| 15 | Pinna apex narrowly rounded or acute but not drawn out into a sharp tailing point. Rhizome short-creeping or erect, sparsely covered in broad dark-brown to black scales. | Blechnum nudum |
| Pinna apex acuminate, drawn out into a sharp tailing point. Rhizome long creeping, densely covered in narrow red-brown scales at the apex.
Back to 14 | Blechnum contiguum |
| 16 | The larger scales on underside of costa brown throughout, no darker spot at their base | Blechnum camfieldii |
| The larger scales on underside of costa brown and usually with a small dark-brown to black spot at their base
Back to 13 | Blechnum howeanum |
