Classification
 Nomenclature
Scientific Name:
Nephrolepis cordifolia (L.) C.Presl, Tent. Pterid. 79 (1836)
Synonymy:
  • Polypodium cordifolium L., Sp. Pl. 1089 (1753) nom. cons.
  • Aspidium cordifolium (L.) Sw., J. Bot. (Schrader) 1800(2): 32 (1801)
Type: Hispaniola, Dominican Republic, prov. de Azua, San José de Ocoa, slope of Loma del Rancho, Ekman H11627, 23 Feb. 1929, K 000590569 (!online), typ. cons. (see Verdcourt 1996)
  • = Polypodium auriculatum L., Sp. Pl. 1088 (1753) nom. rej.
  • Nephrolepis auriculata (L.) Trimen, J. Linn. Soc., Bot. 24: 152 (1887)
Lectotype (selected by Trimen 1887, see Verdcourt 1996): Ceylon, Herb. Hermann 1: 39, No. 383, BM 000621367 (!online)
  • = Aspidium tuberosum Bory ex Willd., Sp. Pl. 5(1), 234 (1810)
  • Nephrodium tuberosum (Bory ex Willd.) Desv., Mém. Soc. Linn. Paris 6: 252 (1827)
  • Nephrolepis tuberosa (Bory ex Willd.) C.Presl, Tent. Pterid. 79 (1836)
Holotype: Réunion, Bory 111, Herb. Willdenow, B-W 19759-01 0 (!online)
Etymology:
From the Latin cordi- (heart-shaped) and folium (leaf), a reference to the auricled bases of the pinnae.
Vernacular Name(s):
erect sword fern; fishbone fern; herringbone fern; ladder fern; tuber ladder fern; tuber sword fern
 Description

Terrestrial ferns. Rhizomes erect, densely scaly, producing long-creeping runners with adventitious buds and tubers. Rhizome scales spreading, narrowly ovate, tapering from a broad base to a filiform apex, 5.5–7.0 mm long, 0.9–1.7 mm wide, peltate, light brown, dull, margins irregularly lacerate at base with ciliate projections. Fronds 260–1130 mm long. Stipes 20–570 mm long, pale brown, brittle, densely scaly. Rachises pale brown, densely scaly; rachis scales spreading, narrowly ovate to linear, light brown, margins irregularly lacerate at base with ciliate projections. Laminae 1-pinnate, narrowly elliptic to linear, tapering to apex; fertile laminae 240–1020 mm long, 30–100 mm wide, yellow-green on both surfaces, herbaceous; lamina surfaces lacking scales or with very scattered hair-like scales, sometimes bearing multicellular hairs. Primary pinnae in 45–110 pairs, not or slightly overlapping; the longest near the middle, 15–53 mm long, 5–9 mm wide, narrowly ovate or oblong with a pointed basal acroscopic lobe, slightly falcate; basal pinnae much reduced; pinna apices obtuse or rounded, margins serrate to deeply lobed, bases short-stalked and unequally auricled. Sori round, close to margin; indusia lunulate, attached at broad base, 0.70.8 mm long. Mean spore size 28–33 μm long, 18–22 μm wide; perispores pale brown, tuberculate.

 Recognition

Nephrolepis cordifolia is a naturalised species that is very similar to the indigenous N. flexuosa. It is distinguished by the presence of tubers on its long-creeping runners, by its more abundantly scaly rhizomes and stipe bases, and by its generally longer and wider laminae (240–1020 mm long, 30–100 mm wide, cf. 170–620 mm long, 18–50 mm wide). The rhizome scales are also longer and wider (5.5–7 mm long, 0.9–1.7 mm wide, cf. 3–5 mm long, 0.2–0.5 mm wide), with lacerate rather than entire bases. Nephrolepis cordifolia is a diploid species (2n = 82) and has smaller spores than the tetraploid N. flexuosa (28–33 μm long, 18–22 μm wide, cf. 36–38.5 μm long, 23–25 μm wide). It is distinguished from both N. brownii and N. exaltata by its lunulate, rather than reniform, indusia.

Plants with pinnatisect apices to some of the primary pinnae are occasionally found and are referable to ‘Plumosa’ (Hoshizaki & Moran 2001). Plants of this cultivar from Orewa and the Waitākere Ranges, Auckland, were illustrated by Large & Farrington 2016, fig. 1b), and have also been collected from urban sites in Hamilton, Tauranga and Wellington. Large & Farrington noted the apparent absence of tubers in this cultivar, but tubers can be seen in at least some collections (see Fig. 12). Large & Farrington also noted that plants were often sterile with a high degree of spore irregularity and abortion, but whether this was due to unsuitable climatic conditions or an indication of hybrid origin was unclear.

 Distribution

North Island: Northland, Auckland, Volcanic Plateau, Gisborne, Southern North Island.

South Island: Western Nelson.

Altitudinal range: 0–240 m.

Nephrolepis cordifolia is widely naturalised in the northern North Island from Northland to the Bay of Plenty and Gisborne, and again in the southern North Island from Whanganui to Wellington. It is confined to coastal and lowland districts, reaching 240 m on Whale Island in the Bay of Plenty. There are records from Golden Bay and Tasman Bay in the South Island.

Occurs naturally in the Neotropics from Cuba to Venezuela, and in the Paleotropics from Madagascar to India, Sri Lanka, China, south-east Asia, Australia (Queensland, New South Wales), Vanuatu, New Caledonia, Samoa and Hawai‘i (Hovenkamp & Miyamoto 2005; de Lange et al. 2005). Naturalised in Central America and Mexico (Mickel & Smith 2004), parts of Africa (Roux 2009), south-east Australia (Bell 1998), Norfolk Island (de Lange et al. 2005) and the Cook Islands (Sykes 2016).

 Habitat

Nephrolepis cordifolia is now a serious environmental weed that occurs not only around current or former sites of human habitation, and on the sides of roads or railways, but also in urban forest remnants and coastal forest. It is common on scoria banks and rough lava, but also on rock walls, the sides of buildings, among boulders and under open pōhutukawa, mānuka, kānuka, Eucalyptus and pine, sometimes on thermally heated soil. Some occurrences possibly result from deliberate plantings undertaken in the mistaken belief that the species is indigenous.

 Biostatus
Exotic
 First Record

Heath & Chinnock (1974). Earliest voucher: AK 289696, 1887, in cultivation; AK 251931, 1928.

 Cytology
 Notes

Plants of Nephrolepis have been widely cultivated in northern New Zealand since the late 19th century, although they were not recorded in the wild until much later, and it is entirely possible that both species and hybrids have occasionally escaped. Further work is needed to determine the status of plants with aborted spores.

 Bibliography
Bell, G.H. 1998: Davalliaceae. In: Flora of Australia. Vol. 48. 434–450.
Biosecurity New Zealand 2012: Regional Pest Management Strategies Database. http://www.biosecurityperformance.maf.govt.nz/
Biosecurity New Zealand 4 Aug 2011: Unwanted Organisms Register. http://www.biosecurity.govt.nz/pests/registers/uor
Biosecurity New Zealand 2008: National Plant Pest Accord. MAF Biosecurity New Zealand, Wellington.
Brownsey, P.J.; Perrie, L.R. 2019: Nephrolepidaceae. In: Breitwieser, I.; Wilton, A.D. (ed.) Flora of New Zealand — Ferns and Lycophytes. Fascicle 26. Manaaki Whenua Press, Lincoln.
de Lange, P.J.; Gardner, R.O.; Sykes, W.R.; Crowcroft, G.M.; Cameron, E.K.; Stalker, F.; Christian, M.L.; Braggins, J.E. 2005: Vascular flora of Norfolk Island: some additions and taxonomic notes. New Zealand Journal of Botany 43(2): 563–596.
de Lange, P.J.; Murray, B.G.; Datson, P.M. 2004: Contributions to a chromosome atlas of the New Zealand flora – 38. Counts for 50 families. New Zealand Journal of Botany 42: 873–904.
Desvaux, N.A. 1827: Prodrome de la famille des fougères. Mémoires de la Société Linnéenne de Paris 6: 171–337.
Heath, E.; Chinnock, R.J. 1974: Ferns and fern allies of New Zealand. Reed, Wellington.
Hobbs, J.; Hatch, T. 1994: Bulbs for New Zealand Gardens. Godwit Press, Auckland.
Hoshizaki, B.J.; Moran, R.C. 2001: Fern Grower’s Manual. Timber Press, Portland, Oregon.
Hovenkamp, P.H.; Miyamoto, F. 2005: A conspectus of the native and naturalized species of Nephrolepis (Nephrolepidaceae) in the world. Blumea 50(2): 279–322. [as Nephrolepis cordifolia (L.) C.Presl var. cordifolia]
Howell, C. 2008: Consolidated list of environmental weeds in New Zealand. DOC Research & Development Series 292: 42.
Large, M.F.; Farrington, L. 2016: The Nephrolepis Boston fern complex (including Nephrolepis exaltata [L.] Schott), Nephrolepidaceae, naturalised in New Zealand. Perspectives in Biosecurity Research Series 2: 1–8.
Linnaeus, C. 1753: Species Plantarum. Impensis Laurentii Salvii, Stockholm.
Mickel, J.T.; Smith, A.R. 2004: The Pteridophytes of Mexico. Memoirs of the New York Botanical Garden 88: 1–1054.
Ministry for Primary Industries 23 Feb 2017: Unwanted Organisms Register. Version 02.01.02. https://www1.maf.govt.nz/uor
Presl, C.B. 1836: Tentamen Pteridographiae. Haase, Prague.
Roux, J.P. 2009: Synopsis of the Lycopodiophyta and Pteridophyta of Africa, Madagascar and neighbouring islands. Strelitzia 23: 1–296.
Swartz, O.P. 1801: Genera et species filicum ordine systematico redactarum. Journal für die Botanik (Schrader) 1800(2): 1–120.
Sykes, W.R. 2016: Flora of the Cook Islands. National Tropical Botanical Garden, Kalaheo, Kauaˋi, Hawaiˋi.
Trimen, H. 1887: Hermann’s Ceylon Herbarium. Journal of the Linnean Society. Botany 24: 129–155.
Verdcourt, B. 1996: Proposals to conserve the name Polypodium cordifolium with a conserved type, and to reject P. auriculatum, in order to stabilize nomenclature in Nephrolepis (Oleandraceae or Nephrolepidaceae). Taxon 45: 539–542.
Willdenow, C.L. 1810: Species Plantarum. Vol. 5 (1). G.C. Nauk, Berlin.