Austroblechnum colensoi


colensoi: Named after William Colenso (7 November 1811 - 10 February 1899) who was a Cornish Christian missionary to New Zealand, and also a printer, botanist, explorer and politician.

Common Name(s)

Colenso's hard fern, peretao, petako

Current Conservation Status

2012 - Not Threatened

Conservation status of New Zealand indigenous vascular plants, 2012
The conservation status of all known New Zealand vascular plant taxa at the rank of species and below were reassessed in 2012 using the New Zealand Threat Classification System (NZTCS). This report includes a statistical summary and brief notes on changes since 2009 and replaces all previous NZTCS lists for vascular plants. Authors: Peter J. de Lange, Jeremy R. Rolfe, Paul D. Champion, Shannel P. Courtney, Peter B. Heenan, John W. Barkla, Ewen K. Cameron, David A. Norton and Rodney A. Hitchmough. File size: 792KB

Previous Conservation Status

2009 - Not Threatened
2004 - Not Threatened


Austroblechnum colensoi (Hook.f.) Gasper et V.A.O.Dittrich



Flora Category

Vascular - Native

NVS Species Code


The National Vegetation Survey (NVS) Databank is a physical archive and electronic databank containing records of over 94,000 vegetation survey plots - including data from over 19,000 permanent plots. NVS maintains a standard set of species code abbreviations that correspond to standard scientific plant names from the Ngä Tipu o Aotearoa - New Zealand Plants database.

Structural Class



Blechnum patersonii (R.Br.) Mett. sensu Allan 1961; Lomaria patersonii R.Br. var. elongata sensu Cheeseman; Lomaria heterophylla Colenso; Blechnum patersonii var. elongatum (Blume) Domin; Lomaria colensoi Hook.f. in Hook.; Blechnum colensoi (Hook. f.) N.A. Wakef.


Endemic. New Zealand: North (from Warawara Forest south), South, Stewart, Chatham and Auckland Islands.


Coastal to montane. Usually within seepages on shaded steep banks, rock overhangs and fringing river gorges; also on sodden ground within cloud forest


Stout fern of damp, shaded places, producing numerous cartilaginous to coriaceous fronds up to 1 m long (usually much less). Rhizomes short-creeping, scaly. Sterile frond stipes 60-400 mm long, base covered in dark red-black to black scales, laminae narrow elliptic, elliptic to almost rhomboid, undivided, 100-350(-800) x 25-600 mm, dark green to glaucous green above, paler beneath, cartilaginous or coriaceous. Sterile pinnae 1-10-paired, 100-200(-800) x 20-40(-80) mm, of similar size except for basal pairs which are reduced to margin flanges, apices tapering, margins smooth, glabrous, bases decurrent. Fertile fronds similar to sterile in stature, extremely slender, the terminal pinnae distinctly larger than the rest.

Similar Taxa

Austroblechnum colensoi has no close relatives in New Zealand, being most similar to A. patersonii of Australia, with which it was once included. It is easily recognised by the dark glaucous green to very dark green sparingly and broadly divided fronds, which are a marked contrast to the very slender fertile fronds


Not applicable (spore producing)

Flower Colours

No Flowers


Not applicable (spore producing)

Propagation Technique

Difficult. Very slow growing. Requires heavily shaded, cool conditions, in permanently moist soil. Will not tolerate drying out.


Not Threatened but very uncommon north of Auckland

Chromosome No.

2n = 122

Endemic Taxon


Endemic Genus


Endemic Family



Perrie et al. (2014) advocated for a broadened circumscription of Blechnaceae whereby a number of genera traditionally recognized as distinct from Blechnum were merged within it. However, this view has not met with universal acceptance (see de Gasper et al. 2016) and does not seem to be followed worldwide (PPG 2016). From a New Zealand perspective the decision to merge Doodia in Blechnum, and rejection of Diploblechnum has not been universally accepted either e.g., Wilcox & Warden (2017), and as such it is considered appropriate to follow world opinion and accept the taxonomy of de Gasper et al. (2016) and recommendations of the PPG (2016). See also the comments by Pyner (2017).



Fact Sheet by P.J. de Lange 7 March 2006. Description based on Brownsey and Dodsworth (2000) supplemented with observations made from herbarium specimens

References and further reading

Brownsey, P.J.; Smith-Dodsworth, J.C. 2000: New Zealand ferns and allied plants. David Bateman Ltd, Auckland

Gasper, A.L.; de Oliveira Dittrich, V.A.; Smith A.R.; Salino, A. 2016:  A classification for Blechnaceae (Polypodiales: Polypodiopsida): New genera, resurrected names, and combinations. Phytotaxa 275: 191–227.

Perrie, L.R.; Wilson, R.K.; Shepherd, L.D.; Ohlsen, D.J.; Batty, E.L.; Brownsey, P.J.; Bayly, M.J. 2014: Molecular phylogenetics and generic taxonomy of Blechnaceae ferns. Taxon 63(4): 745-758.

PPG 1: The Pteridophyte Phylogeny Group 2016: A community-derived classification for extant lycophytes and ferns. Journal of Systematics and Evolution 54: 563-603.

Pyner, T. 2017: A new classification of Blechnum. British Pteridological Society. https://ebps.org.uk/new-classification-blechnum/

Wilcox, M.; Warden, J. 2017: Botany of Hillsborough coast bush reserves, Manukau Harbour, Auckland. Auckland Botanical Society Journal 72: 32-46.


This page last updated on 5 Sep 2017