Asplenium decurrens
Willd.Rhizome short, thick, covered with shiny purplish-brown, translucent scales tapering to long, fine points. Fronds clustered, erect, 8–60 cm long; scales at base of frond similar to those on rhizome, smaller scales scattered on rachis and midveins, particularly on ventral surface, sometimes bubble-like. Stipe fleshy, green above, brown and flat towards base, groove developing towards lamina; old stipe bases persistent. Lamina once pinnate, oblong, thick, tough and fleshy, dull green; rachis grooved with raised central rib continuing as raised midvein of terminal pinna. Pinnae shortly stalked, 4–15 pairs, oblong to ovate, mostly 15–65 mm long, sometimes lobed near base; base asymmetrically wedge-shaped, decurrent on edge or rachis; margins bluntly toothed, thickened; apex blunt to acute; midvein raised, others obscure. Sori linear-oblong, oblique to midvein, not reaching margin; indusium oblong, opening towards midrib.
VVP, GipP, EGL, WPro. Also WA, NSW, Tas. New Zealand, South America and many Subantarctic and Pacific islands. Usually grows among coastal rocks within reach of salt spray, but also sheltered in coastal scrub. Mostly on granite (e.g. Phillip Is., islands near Wilsons Promontory, Rame Head and Gabo Is. in the far east), but also on basalt at Lady Julia Percy Is. in the far west.
This species was previously included within the similar coastal species, A. obtusatum G.Forst. as subsp. northlandicum Brownsey. It has narrower scales and larger spores than A. obtusatum. The larger spores in A. decurrens is assumed to be indicative of this species being a higher ploidy than A. obtusatum given that a New Zealand plant currently included in A. decurrens (Brownsey & Perrie 2018) has an octoploid chromosome count, whereas A. obtusatum is tetraploid (Brownsey 1977). Asplenium decurrens was shown by nuclear DNA sequence data to be most likely an allooctoploid with A. obtusatum and another unidentified species as its parents (Shepherd et al. 2008). It is general practice in fern taxonomy to recognise allopolyploids at species rank (Barrington et al. 1989), which is why it is here recognised as a separate species. This species has previously been recognised in New Zealand as A. northlandicum (Brownsey) Ogle, but A. decurrens is the earlier name for this species under its current circumscription and takes priority. There are subtle differences between Australian and New Zealand plants currently included in A. decurrens, such as fenestrate spores in Australian plants (Brownsey 1998) and differences in chloroplast DNA sequences (Ohlsen et al. 2014). Consequently, whether New Zealand plants should continue to be treated as conspecific with Australian A. decurrens requires confirmation.
Hybridises with A. flaccidum on Wilsons Promontory and adjacent islands (Brownsey 1983). Early reports of these putative hybrids were misidentified as A. scleroprium Hombron (which, interestingly, can only be easily separated from hybrids between the A. obtusatum complex and A. flaccidum by its fertile spores: see Brownsey 1983). Asplenium decurrens reportedly also hybridises with A. bulbiferum (e.g. Flinders Is.).
SpinningBarrington, D.S.; Haufler, C.H.; Werth, C.R. (1989). Hybridisation, reticulation and species concepts in the ferns. American Fern Journal ** 79**: 55–64.
Brownsey, P.J. (1977). A taxonomic revision of the New Zealand species of Asplenium. *New Zealand Journal of Botany * 15: 39–86.
Brownsey, P.J. (1983). Asplenium terrestre and two Asplenium hybrids: new fern records for Australia. Muelleria 5: 219–221.
Brownsey, P.J.; Perrie, L.R. (2018). Aspleniaceae. In: Breitwieser, I.; Wilton, A.D., Flora of New Zealand-Ferns and Lycophytes. Fascicle 18., pp. –. Manaaki Whenua Press, Lincoln.
Ohlsen, D.J. (2020). Asplenium. In: Kodela, P.G., Flora of Australia, pp. –. Australian Biological Resources Study, Canberra.
Ohlsen, D.J., Perrie, L.R., Shepherd, L.D., Brownsey, P,J.; Bayly, M. (2014). Phylogeny of the fern family Aspleniaceae in Australasia and the south-west Pacific. Australian Systematic Botany 27 27: 355–371.
Shepherd, L.D.; Perrie, L.R.; Brownsey, P.J. (2008). Low-copy nuclear DNA sequences reveal a predominance of allopolyploids in a New Zealand Asplenium fern complex. Molecular Phylogenetics and Evolution 49: 240–248.
