Journal Number 97
November 2005


EDITORIAL

Nematoceras dienema
By Ian St George

 

N dienema

 

In a cupped leaf, Nematoceras dienema from
Macquarie Island with those characteristic,
chunky, upstanding tepals.

Australia's only Nematoceras.

     

The Antipodes Subantarctic Islands tundra ecoregion consists of five island groups spread across the Southern Ocean: Bounty Islands, Auckland Islands, Antipodes Islands, Campbell Island, and Macquarie Island. Their remoteness provides important resting and breeding areas for marine mammals and seabirds. All the islands are Nature Reserves and listed as World Heritage Sites, but introduced animals, especially mammalian predators, are of serious concern [1].

These islands range in latitude from the cold temperate zone (Macquarie Island) to the cool temperate zone for the others.

The climate on all is wet, cold, and windy. They are lashed by westerly gales and cold fronts: it rains more than 300 days a year. Apart from the Bounty isles, the islands administered by New Zealand's DoC support trees and woody plants. Further to the south, Macquarie Island has a mean annual temperature below 5°C and woody plants do not grow there. It is administered by the Tasmanian Parks and Wildlife Service.

     
Habitat  

Habitat shot: "Beach terrace on the west coast
of Macquarie Island: C. macranthus (sic) grows
in the wet bog communities shown above the
line of tussocks in the middle ground"

     

While these islands are species poor, reflecting the high latitude, the flora include species at the limit
of their ecological tolerance and a high number of endemics. Many plants found at or near sea level
here are also found in New Zealand subalpine vegetation.

Macquarie Island's maximum altitude is 433m. There is a central plateau covering most of the land
area, with a narrow coastal strip surrounding some parts. The vegetation is primarily tussock, short
tussock grassland, or feldmark vegetation. Cushion plants are common in exposed sites, and bogs
and mires are common throughout.

     
N dienema  

 

Grown in Tasmania,
photo Les Rubenach,
supplied by Helene Wild.
   
     

Introduced weka and cats have been eradicated from Macquarie Island. Mice, ship rats, and rabbits
persist. Rats still prey on the eggs of burrowing petrels and prions, and despite a huge reduction in
rabbit numbers since myxomatosis in 1978, they still kill large areas of tussock and megaherb
vegetation [2].

There are no trees on Macquarie Island, but there are 45 species of vascular plants and many moss
and lichen species.

Three plant species are endemic to Macquarie Island: the Cushion Plant Azorella macquariensis, the
orchid Nematoceras dienema (Corybas dienemus) and a salt tolerant species Puccinellia macquariensis [1].

Nematoceras dienema (dienemos = windswept) was discovered by Brown and colleagues who took it
to be Corybas macranthus; they described (and illustrated) their discovery in 1978 [3].

Plants collected later by JR Croft were taken back to Canberra, where "The Visitor Centre at the Gardens
set up a delicatessen refrigerator, put in some soil and held a 'life in the fridge' display with much success. One disappointment was the shy little Corybas orchid. It would not grow…".

     
Photo from Brown et al  

 

Photo from Brown et al    
     

It was described by David Jones (who had predicted it would be a new species) in 1993 [4].

His Latin description reads (translated by Dan Hatch), "Related to Corybas macranthus, from which it is separated by the thick, semi-erect leaf, which at flowering forms a cup. Flower small, semi-erect, pale green with red-purple markings; inserted on a distinct peduncle into the heart-shaped base of the leaf."

The entry in Flora Australia reads, "Plant 3-5cm tall at flowering. Leaf orbicular, 1.5-2.5cm diam., dark green above, pellucid beneath, cupular and semi-erect at flowering, apiculate, thick-textured. Flowers pale green and reddish purple, semi-erect in cordate base of leaf. Dorsal sepal linear-oblanceolate, acuminate, cucullate over labellum tube; lateral sepals and petals filiform, long-acuminate, subequal, stiffly erect. Labellum tubular at base; lateral margins flared to incurved, irregularly crenate…. This species can be immediately distinguished by the pale green and red, semi-erect flowers which sit in the cordate base of the leaf".

Distinguished from what, one might ask? seaweed? megaherbs? certainly not from other Nematoceras.

Laursen and his colleagues from the University of Alaska examined the roots of vascular plants from Macquarie Island to determine their mycorrhizal status. N. dienema showed typical orchid mycorrhizae [5].

Jones, Clements and Molloy [6] renamed it Nematoceras dienema in 2002.

Szlachetko reclassified Corybas in 2003 and included C. dienemus in his reinstated Corysanthes [6].

Mary Skotnicki and Mark Clements are conducting a new study called "Biodiversity, biogeography, reproduction and conservation of the Macquarie Island orchid Nematocerus (Corybas) dienema".

Nematoceras dienema is the only known orchid in the Subantarctic region. How on earth did it get there ?

Brown and colleagues thought it was N. macrantha and speculated that its seeds had been carried from New Zealand by wind, by shared seabirds, or by man.

But it isn't N. macrantha and it has not been discovered anywhere else. Where on earth did it come from? Not from Australia (no Nematoceras have been found there). From southeast Asia, the homelands of Nematoceras? it seems an awfully long way. From Gondwanaland? No: Macquarie Island rose recently (600,000 yrs ago) from the seabed.

From the nearby cold temperate islands (Bounty, Antipodes, Campbell, Auckland Is)? There
remains some doubt as to the identity of Nematoceras from these sites, but accoding to Edgar,
all are N. triloba agg.

     
Drawing by D.Boyer  

 

Drawing by D. Boyer    
     

From New Zealand? Bruce Irwin wrote, "It has always puzzled me that a fragile orchid apparently quite
unlike any New Zealand species of the genus, and very different from any of the Australian species
should evolve on a smallish scrap of land in latitudes where no other orchid can exist. From what
could it evolve? It seems that an identical or at least very similar Corybas in NZ has to be the source"
[pers.comm.].

Perhaps, though, whatever it evolved from in NZ may itself have evolved into something completely
different. Something more like, e.g., N. longipetala.

Eric Scanlen describes in this issue, a plant discovered by Steven Reekie at an exposed site on the
West Coast, which he believes has affinities with N. dienema. It must be said that its flower is also
very much like immature N. longipetala, which were found a few metres away, higher up in what
Steve thought was the same colony.

Whatever it turns out to be, its structure - with the short stature, stout tepals and cupped leaf adapted
to the exposed site - may give us a hint about why, if not whence, N. dienema evolved the way it has.
 


References


1. http://www.deh.gov.au/biodiversity/threatened/publications/recovery/albatross/habitat.html
2. Laursen, GA; Treu, R; Seppelt, RD; Stephenson, SL. Mycorrhizal assessment of vascular plants from subantarctic
    Macquarie Island. Arct. Alp. Res. 29: 483-491. (1997).(http://instaar.colorado.edu/AAAR/volume29/29-4abs.html).
3. Brown MJ, JF Jenkin, NP Brothers, GR Copson. Corybas macranthus (Hook.f.) Reichb.f. (Orchidaceae) a new record
    for Macquarie Island. NZ J Bot 16: 405-7 (1978).
4. Jones DL. Corybas dienemus sp.nov. Fl. Australia 50: 572 (1993) (see also p528).
5. http://www.worldwildlife.org/wildworld/profiles/terrestrial/aa/aa1101_full.html
6. DL Jones et al. Nomenclatural notes arising from studies into the tribe Diurideae (Orchidaceae). Orchadian
    13(10): 437-468 (2002).
7. Corysanthes dienema (DL Jones) Szlach. in Richardiana 3(2): 98. 2003: Corybas dienemus.
8. Draft management plan for Macquarie island (http://www.parks.tas.gov.au/publications/tech/macquarie/macquarie.pdf).

 

 

 

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