Classification
 Nomenclature
Scientific Name:
Cyclosorus interruptus (Willd.) H.Itô, Bot. Mag. (Tokyo) 51: 714, f. 9 (1937)
Synonymy:
  • Pteris interrupta Willd., Phytographia 13, t. 10, f. 1 (1794)
  • Thelypteris interrupta (Willd.) K.Iwats., J. Jap. Bot. 38: 314 (1963)
Lectotype (selected by Mazumdar 2016): Plate 1, fig. 1 in Willdenow, Phytographia (1794). Epiptype (selected by Mazumdar 2016): India, Tamil Nadu [Madras], Aug. 1794, Rottler ex Klein s.n., Herb. Willd. no. 19770011, B (!online), isoepitype Herb. Willd. no. 19770012, B (!online).
  • = Nephrodium propinquum R.Br., Prodr. Fl. Nov. Holland. 148 (1810)
Lectotype (selected by Brownsey & Perrie 2016): New Holland [Australia], Nova Cambria australis [now Queensland] prope [near] Endeavour River, J. Banks & D. Solander s.n., 1770, BM 001044504!
  • = Nephrodium inaequilaterum Colenso, Trans. & Proc. New Zealand Inst. 20: 229 (1888)
Lectotype (chosen by Allan 1961): Taupo, C.J. Norton, Herb. W. Colenso, WELT P003345!
Etymology:
From the Latin interruptus (interrupted).
 Description

Rhizomes long-creeping, up to 115 mm long (in herbarium specimens) with stipes arising 5–30 mm apart, 1.5–4 mm diameter, bearing scattered scales. Rhizome scales ovate to broadly ovate, 1–3 mm long, 0.5–1.5 mm wide, pale to dark brown, entire. Fronds 225–1450 mm long, held stiffly upright. Stipes 120–970 mm long, yellow-brown to chestnut-brown, almost black at base, glabrous or scaly near base, slightly polished. Laminae 1-pinnate, usually elliptic or ovate, sometimes narrowly, rarely broadly so, abruptly narrowed to a pinnatifid apex, 115–580 mm long, 35–215 mm wide, dull green on both surfaces or sometimes lighter on abaxial surface, coriaceous. Ovate or broadly ovate, pale brown scales with hairy margins on abaxial surface of pinna midribs and costae; colourless, acicular hairs up to 0.4 mm long on both surfaces of the costae and veins; spherical orange glands variably present on abaxial surfaces of costae and veins. Primary pinnae in 6–18 pairs below the pinnatifid apex, widely spaced especially proximally, narrowly elliptic; the longest at or below the middle, short-stalked, 42–150 mm long, 6–18 mm wide; the basal pair not or scarcely reduced in length. Primary pinnae divided ⅓ to ½ to the midrib; ultimate segments 3–10 mm long, 2.5–6 mm wide; apices acute and bluntly apiculate, margins entire. Basal veins on adjacent pinna segments joining, unbranched in each ultimate pinna segment. Sori round, in one row either side of midrib away from pinna margins; indusia reniform, 0.5–0.9 mm diameter, bearing acicular or rarely capitate hairs or almost glabrous.

 Recognition

Cyclosorus interruptus is recognised by its long-creeping rhizomes, erect and leathery fronds, primary pinnae divided one-third to halfway to the midrib with acute segments, basal pair of pinnae not reduced, veins in adjacent segments joining, indumentum on the abaxial lamina surfaces comprising broad scales, acicular hairs and spherical orange glands, and indusia usually bearing acicular hairs or sometimes glabrous. Plants vary considerably in size; the largest, with greatly extended stipes (longer than the laminae), occur in swamps in the Far North, whilst stunted plants are found on thermal soils in the central North Island with much smaller fronds and shorter rhizomes.

 Distribution

North Island: Northland, Auckland, Volcanic Plateau.

Altitudinal range:  0–600 m.

Cyclosorus interruptus occurs in coastal and lowland areas of the North Island from Te Paki to Kāwhia and the Bay of Plenty, and throughout the geothermal region from Whakatāne to Tokaanu where it extends locally into montane areas. It grows from sea level to about 600 m near Wairakei.

Also widespread in the tropics and subtropics of the Americas, Africa, India, Asia, Australia and most of the islands of the Pacific, including Hawai‘i.

 Habitat

Occurs in swamps, on peaty soils and lake margins in the northern part of its distribution, and on heated soil near hot springs and streams, or in swamps, in geothermal regions, sometimes under mānuka, and kānuka. In the Waikato it is also found under willows (Salix cinerea and S. fragilis). It is often associated with Typha orientalis, Phormium tenax, Isachne globosa, Machaerina juncea, Carex spp., Juncus spp., Schoenus brevifolius, Thelypteris confluens and Blechnum minus, and with Christella dentata, Lycopodiella cernua and Nephrolepis flexuosa in thermal areas.

 Biostatus
Indigenous (Non-endemic)

The species was given a conservation status of 'At Risk / Declining' by de Lange et al. (2013).

Leach (2005) suggested that Cyclosorus interruptus might have been introduced to New Zealand by early Polynesian settlers, because it grows in abandoned taro pondfields in the Pacific Islands and could have been introduced with taro. Against this is the likelihood of self-dispersal, given the large number of fern species that are indigenous to New Zealand and shared with Australia and/or the Pacific Islands.

 Cytology

n = 36 (Brownlie 1961, as Cyclosorus gongylodes).

 Notes

The names Polypodium unitum L. and Aspidium gongylodes Schkuhr, and combinations based on them used in earlier Flora treatments (notably Nephrodium unitum, Cyclosorus gongylodes, Dryopteris gongylodes and Thelypteris gongylodes) are misidentifications of Cyclosorus interruptus (see Holttum 1977; Bostock 1998).

 Bibliography
Bostock, P.D. 1998: Thelypteridaceae. In: Flora of Australia. Vol. 48. 327–358.
Brown, R. 1810: Prodromus Florae Novae Hollandiae et Insulae Van-Diemen. Johnson, London.
Brownlie, G. 1961: Additional chromosome numbers – New Zealand ferns. Transactions of the Royal Society of New Zealand. Botany 1: 1–4.
Brownsey, P.J.; Perrie, L.R. 2016: Taxonomic notes on the New Zealand flora: lectotypes in the fern family Thelypteridaceae. New Zealand Journal of Botany 54(1): 87–91.
Brownsey, P.J.; Smith-Dodsworth, J.C. 2000: New Zealand ferns and allied plants. Edition 2. David Bateman, Auckland.
Colenso, W. 1888: On newly discovered and imperfectly known ferns of New Zealand, with critical observations. Transactions and Proceedings of the New Zealand Institute 20: 212–234.
de Lange, P.J.; Norton, D.A.; Courtney, S.P.; Heenan, P.B.; Barkla, J.W.; Cameron, E.K.; Hitchmough, R.; Townsend, A.J. 2009: Threatened and uncommon plants of New Zealand (2008 revision). New Zealand Journal of Botany 47: 61–96. [Declining]
de Lange, P.J.; Norton, D.A.; Heenan, P.B.; Courtney, S.P.; Molloy, B.P.J.; Ogle, C.C.; Rance, B.D. 2004: Threatened and uncommon plants of New Zealand. New Zealand Journal of Botany 42(1): 45–76.
de Lange, P.J.; Rolfe, J.R.; Barkla J.W.; Courtney, S.P.; Champion, P.D.; Perrie, L.R.; Beadel, S.N.; Ford, K.A.; Breitwieser, I.; Schönberger, I.; Hindmarsh-Walls, R.; Heenan, P.B.; Ladley, K. 2018: Conservation status of New Zealand indigenous vascular plants, 2017. New Zealand Threat Classification Series No. 22. [Declining]
de Lange, P.J.; Rolfe, J.R.; Champion, P.D.; Courtney, S.P.; Heenan, P.B.; Barkla, J.W.; Cameron, E.K.; Norton, D.A.; Hitchmough, R.A. 2013: Conservation status of New Zealand indigenous vascular plants, 2012. New Zealand Threat Classification Series 3. Department of Conservation, Wellington. [Declining]
Holttum, R.E. 1977: The family Thelypteridaceae in the Pacific and Australasia. Allertonia 1: 169–234.
Itô, H. 1937: Filices Japonenses VI. Botanical Magazine (Tokyo) 51: 709–714.
Iwatsuki, K. 1963: Thelypteroid ferns of Thailand and Laos collected by Dr. T. Tuyama in 1957-58. Journal of Japanese Botany 38: 313–315.
Leach, H. 2005: Gardens without weeds? Pre-European Maori gardens and inadvertent introductions. New Zealand Journal of Botany 43: 271–284.
Mazumdar, J. 2016: Retypifications of Adiantum incisum (Pteridaceae) and Pteris interrupta (Thelypteridaceae). Fern Gazette 20: 143–145.
Willdenow, C.L. 1794: Phytographia seu descriptio rariorum minus cognitarum plantarum. Walther, Erlangen.