C. Michael Hogan PhD
April 30, 2009
This New Zealand endemic is widely distributed in North, South, Chatham and Stewart Islands, sometimes becoming the dominant understory plant in coastal montane forests. It is present in a wide variety of forest types from dry lowland to wet montane to Stewart Island rainforest. The characteristic shape of a near vertical array of hard sterile fronds gives this fern its appearance of a tiara or crown.
B. discolor is one of the most broadly distributed ferns in New Zealand, having adapted to many soil types, microclimates and overstory dominants. Seen throughout the North Island and Stewart Island, it is present in coastal forests throughout South Island, save for limited stretches of the eastern coast. Notably in the western part of South Island, Crown Fern ranges from lowland coastal forests through their continuous extent into higher elevations of the Southern Alps. In particular on South Island it is found widely in the watersheds of Milford, Doubtful and Marlborough Sounds and within Tongariro, Kahurangi, Paparoa, Westland, Fiordland (including the Lake Te Anau catchment) and Abel Tasman National Parks. It is also a prominent species within these South Island watersheds: Grey, Hokitika, Clutha, Mataura Rivers; it is additionally widespread in the middle reach of the Rakaia River catchment. It is also found widely in the Rakiura National Park on Stewart Island including along the Rakiura Track.
On North Island B. discolor is found almost throughout, but notably within the Whanganui National Park and more broadly the Whanganui River catchment basin. Also on North Island Crown Fern is found widely within Urewera National Park and specifically within the catchments of Lake Waikaremoana and Lake Waikareiti. Further as to notable North Island occurrences, B. discolor is within the old growth forests of Egmont National park. In central North Island it is found in the Lake Taupo catchment and throughout the rainforests of Tongariro National Park. Another notable occurrence on North Island is within the Urewera National Park, including the forested areas of the Lake Waikaremoana and Lake Waikareiti basins.
Crown Fern is found in several distinct habitats, including mixed hardwood podocarp forests of Southland; mixed nothofagus podocarp forests on the northern part of South Island, Westland podocarp/broadleaf associations and Stewart Island podocarp/mixed hardwood forests.
An example North Island habitat is within the Hamilton Ecological District, (Clarkson et al., 2007) where B. discolor is a dominant understory element with Nothofagus truncata and rimu overstory. Associate ferns in this association are Blechnum filiforme, Asplenium flaccidum, Doodia media, Hymenophyllum demissum, Microsorum pustulatum and M. scandens. Associate shrubs here are Olearia ranii, Alseuosmia quercifolia, Coprosma arborea, C. rhamnoides and C. spathulata. The viny Clematis ternifolia and Metrosideros perforata are also found here. Grasses Astrelia trinervia and Eriolaena avenacea are present as well. This entire plant association is replicated in the nearby Pukemokemoke Reserve
Habitat on the northern South Island is epitomised by the Nelson Lakes National Park, dominated by canopy species of beech and podocarps.(Wardle, 1991) On the moist colluvial slopes are found red beech and silver beech, along with miro and rimu podocarps, with Crown Fern an important understory species. Associate forest floor species are Kunzea ericoides, Coprosma microcarpa, Cyathodes fasciculata and Cyathodes juniperina along with understory mats of Dicranoloma and Leucobryum. Ocean facing slopes may also have the diminutive tree Coprosma linariifolia. This forest type is specifically seen as well in the Sabine Valley of the Spenser Ecological Reserve. At higher elevations where drainage is compromised, mountain beech along with Phyllocladus alpinus and Archeria traversii may be added associates.
Central Westland of South Island forms another significant habitat for Crown Fern. Here are the most extensive continuous reaches of podocarp/broadleaf forests in New Zealand. The overstory includes miro, rimu, southern rata and mountain totara. The lower story consists of Cyathea smithii, Dicksonia squarrosa, Myrsine australis and Pseudopanax simplex. Crown Fern is dominant in the fern tier. In these Westland forests there are numerous epiphytic associates growing on tree trunks, tree fern bases and terrestrially; some of the common epiphyte associates are: Asplenium polyodon, Trichomanes reniforme, Ctenopteris heterophylla, Grammitis billardierei, Tmesipteris tannensis, Lycopodium varium, Astelia solandri, dendrobium cunninghamii and Luzuriaga parviflora. Further understory tier associates are Blechnum procerum, Rumohra adiantiformis, Ascarina lucida, Pseudowintera colorata, Pseudopanax colensoi, P. edgerleyi, P. crassifolius, Myrsine divaricata, Coprosma lucida, C. colensoi, Nertera depressa, Libertia pulchella, Quintinia acutifolia, Rubus cissoides, Elaeocarpus hookerianus and Neomyrtus pedunculata.
Within the mixed hardwood/podocarp lowland forests of Ulva and Stewart Islands, the Crown Fern is not as dominant an understory element as habitats farther north; however, it is associated with great biodiversity in these Rakiura climax forests, whose composition is likely little altered over the last 65 million years. Dominant canopy species include rimu, miro, lancewood, southern rata and Hall's totara.
The fern diversity in Rakiura, particularly Ulva Island, rivals any location on Earth, including many notable Hymenophyllum species. Fern associates in Rakiura include Blechnum blechnoides, B. durum, B. chambersii, B. colensoi B. fluviatile, B.nigrum, B. novae-zelandiae, B. vulcanicum, B. penna-marina, Polystichum vestitum and P. richardii. Other lower plants I observed in association with Crown Fern were Mniodendron dendroides, Tmesipteris elongata, Asplenium obtusatum, A. bulbiferum and Pteridium esculentum. The tree fern Cyathea medullaris is found in this association as well.
Further understory associates I logged specifically on the Ulva Island forest floor were Earina mucronata, E. autumnalis, Pterostylis auriculata, Dendrobium cunninghamii, Winika cunninghamii, Rhipogonum scandens, Stilbocarpa lyallii, Olearia hectori, Carpodetus serratus, Dracophyllum longifolium and Aristotelia serrata. Birdlife I observed on the predator-free Ulva Island in this forest association included Weka, Tomtit, New Zealand Robin, New Zealand Fantail, New Zealand Bellbird, New Zealand Brown Creeper.and Saddleback.
The rhizome of B. discolor is erect with elongated elliptical fronds attaining a length of one metre and a trunk of 15 to 30 cm in diameter. (Olsen, 2007) Caudices are robust with entangled aerial root mats and associated non-living frond bases. Extensive colonies of the species may exist inter-connected by complex rhizome geometries. The singly pinnate sterile fronds are a darker glossy green colour on the top side compared to the paler gray-green underside. Each frond has 30 to 50 pairs of obviously veined pinnae Sterile fronds have stipes that vary from five to 20 cm in length. (Metcalf, 2003) The fertile fronds are marginally longer than the sterile, and stand somewhat more erect. For some individuals the fertile fronds are sterile near the mid-rib along part of the pinna, and then manifest fertile elements near the pinna tips, leading to a bizarre appearance. The elegant vase shaped array of the sterile fronds forms the iconic shape of the Crown Fern.
* Bruce D. Clarkson, Beverley R. Clarkson and Theresa M. Downs. 2007. Indigenous Vegetation Types of Hamilton Ecological District, University of Waikato, CBER contract report 58: accession 3105
* Peter Wardle. 1991. Vegetation of New Zealand, Published by CUP Archive, 672 pages ISBN 0521258731
* C. Michael Hogan. 2009. Yellow-eyed Penguin: Megadyptes antipodes, GlobalTwitcher.com, ed. Nicklas Stromberg
* Sue Olsen. 2007. Encyclopedia of Garden Ferns, Timber Press, 444 pages ISBN 0881928194
* Lawrie Metcalf. 2003. Ferns of New Zealand, New Holland Publishers, 132 pages