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Interesting Chatham Island Mosses
Encalyptra rhaptocarpa - This
moss has a world wide distribution. It is usually found in montane to alpine
areas where it invariably grows on limestone and marble. In New Zealand it is
very uncommon and until recently was only known in the North Island from the
Ruahine, and in the South Island from scattered sites in Arthur and Owen ranges
(north-west Nelson) and from Fiordland. Earlier this year this moss was
recognised from a gathering made from the sinkhole of Walkemup (Hakepa Hill), Pitt Island.
Walkemup is comprised of trachyte which is a feldspar rich volcanic rock. The
occurrence of this moss on Walkemup is therefore most unusual, though some
forms of feldspar can be very rich in calcium one of the key elements
associated with limestone and marble.
Macromitrium ramsayae has the current distinction of being the only bryophyte considered endemic
to the Chatham Islands. Like most of the endemic
Chatham Island flowering plants and ferns it is
widespread and common, typically forming dense, dark green, velvety mats on
trunks and lower branches of kopi (Corynocarpus
laevigatus), karamu (Coprosma chathamica)
and matipo (Myrsine chathamica) trees
within coastal forest. It also occurs abundantly on basalt outcrops on the
southern coast and it has been recorded occasionally from schist outcrops. For
some reason this moss is especially common along the shores of Te Whanga and
also on the coastal cliffs of the southern tablelands.
Other
interesting species of Macromitrium have also been recorded from the Chatham Islands.
Among these, M. brevicaule, is a
species with dark green or yellow-green leaves with dark brown undersides and a
preference for growing on shaded rock surfaces in coastal forest. Its presence
on the Chatham Islands is noteworthy because
it has previously been recorded in New Zealand only from northern
offshore islands and coastal heads from the vicinity of the Coromandel Peninsula
north to about Te Paki. It is also very common on Raoul
Island in the Kermadec Islands
group.
Archidium elatum, recently discovered
growing on a basalt bluff at Otauwae
Covenant, is one of least known mosses in the New Zealand flora. It is a New Zealand endemic species in a
morphologically very unusual and isolated family. Apart from the Otauwae
population, A. elatum has only been
certainly recorded from New Zealand
at Ahipara and Moturoa Island (including the nearby Black Rocks) in North Auckland. It
is likely that the Ahipara population (from which the type was collected in
1931) is now extinct. This very rare
species is best recognised by the zig-zag appearance of its stems with numerous
innovative branches, its wide-spreading, rigid, strongly costate, and
triangular-lanceolate leaves, and its occurrence on coastal rocks. It is not known to fruit. Archidium
elatum is regarded as a threatened species.
However, it is possibly more common than these records suggest as it is
inconspicuous and perhaps overlooked by collectors.
One
of New Zealand's larger moss
genera is Fissidens of which 19
species have been recorded from the Chatham Islands.
One of these, Fissidens oblongifolius var. oblongifolius is an uncommon moss that had previously been recorded
from a handful of sites in northern New Zealand
from Te Paki southward to Rangitoto Island, and it is also on Raoul
Island in the Kermadec Island
group. Apparently favouring dripping wet clay banks or rock overhangs, on
Chatham Island it has been found on basalt rock and clay under remnant mahoe (Melicytus chathamicus)/hoho (Pseudopanax chathamicus) forest within
the upper Makara River gorge. Fissidens oblongifolius var. hyophilus is a close relative that in New Zealand has
a mostly northern, and typically offshore island distribution, with a peculiar
southern Wellington
and coastal Kaikoura disjunction. Usually found within the root mats and lower
portions of tree and fern trunks, it is so far known from Chatham island growing on damp, rotten
limestone at the back of small caves and recesses along the eastern shoreline
of Te Whanga. On Pitt
Island the aquatic Fissidens integerrimus has also been
found, growing on the top most portion of the Waipapaku Waterfall at Second
Water. This threatened species is extremely uncommon in Australia and New Zealand.
Interestingly it is always found in association with basalt rock.
The
dark tannin-stained streams, rivers and lakes of Chatham Island
are possibly the last place one would expect to find a diverse moss flora. Nevertheless,
in such places have been found two aquatic mosses of particular interest: Fissidens berteroi, and Blindia immersa. Fissidens berteroi is a dark green to blackish green, feathery aquatic
species that seems to require deeply shaded slow to quickly flowing water. In New Zealand it
is considered to be threatened and is known from scattered, mostly historic,
sites in the North and South
Islands. There are several reasonably large
populations recorded from Auckland
City and Masterton. On the Chathams
it has been found in its usual riparian habitat (at the Mangatukurewa (Nairn River)
and Wairarapa Creek) and also from the bottom of Tennants Lake.
Blindia immersa is an impressive
aquatic moss, forming dark golden-brown to blackish
green, wiry, and feathery strands of up to 180 mm. It often occurs at the base of waterfalls but it can also occur
on sand and silt in slower moving streams.
It is a New Zealand
endemic, known from a small number of scattered localities in western parts of
the South Island, and on Stewart and Auckland Islands. On Chatham Island
it has been collected from basalt boulders submerged in a fast flowing section
of the Makara River.
Another
Chatham Island moss with southern affinities is Muelleriella crassifolia. The genus Muelleriella is austral in distribution and is restricted to coastal rocks at sites subject
to flooding at extreme high tide or within the salt spray zone. All four
species in the genus are obligatory halophiles and three of the species occur
in the New Zealand Botanical Region. On
the Chathams, M. crassifolia is known only from Ocean Bay,
where it forms compact black cushions up to 50 mm across on schist rocks
emerging from the sea; the spores here are unusual, being multicellular and up
to 100 µm in diameter. Outside the Chathams this
salt-tolerant moss has been recorded from four localities on the Otago coast,
as well as on Stewart, Snares, Auckland,
Campbell and Macquarie Islands, and southern South
America and parts of Antarctica
Two
particularly interesting recent Chatham
discoveries both belong to the pan-tropical family Calymperaceae. Calymperes
tenerum is a widespread in the
Pacific, Southeast Asia (extending west to India) and
northern Australia. It has also been reported from scattered
western hemisphere tropical localities.
In the islands of Polynesia it occupies
a range of substrates but it is most commonly found on the trunks of coconut
palms or on coconut husks. It has
recently been found growing on the bark near the base of Coprosma chathamica at
the Sweetwater Covenant on the Southern Tablelands and on Pitt Island
at Waipaua where it grew on nikau (Rhopalostylis
sapida) and hoho (Pseudopanax
chathamicus). C. tenerum produces characteristic
globose clusters of transversely septate gemmae on its leaf tips; these
undoubtedly play a role in the dispersal of this widespread species. For a
while the only known site for this species in New Zealand was the Chatham Islands where it reaches its world southern
limit. However in May 2009 this species was also found on Raoul Island.
Syrrhopodon armatus, a very rare species in New Zealand, is the second species
of Calymperaceae recently documented from the Chathams.
S. armatus is a rather small pale
white- or brownish-green plant. Its
leaves are very strongly curved when dry and have a large window (or
"cancellinae") of thin-walled, pellucid cells near their base and
characteristic long, unicellular,wide-spreading to reflexed spines on their
lower margins. Multicellular gemmae are
borne in yellow-green masses at the leaf tips.
The marginal spines are the "armature" refered to in the specific
epithet. On tiny Rabbit Island
in the Chathams
S. armatus is associated with petrel
burrows and this occurrence mirrors one in the Poor Knights
Islands. A second Chatham Islands
collection is from a tree fern trunk at the head waters
of the Wairarapa Creek. Elsewhere in the
New Zealand Botanical Region S. armatus is documented only from the Kermadec's and Poor Knights, a few places
in
eastern Northland, at Hot Water Beach and near Pauanui on the
Coromandel Peninsula. The species is widespread in the Old World
tropics and is reputed to be the "most common
and widespread member of the genus Syrrhopodon in Australia"
by the authors of a recent taxonomic study.
One is tempted to speculate
on the role the pelagic birds such as petrels might have played transporting
these mainly tropical species to the Chathams.
Two other tropical mosses deserve mention. The
first is Ectropothecium sandwichense which carpets boulders and logs along stream ways in a rich golden-yellow turf.
This species is the typical moss one sees in the valley and ravines of tropical
Pacific islands. In New
Zealand it is most common on Raoul Island,
and is other wise known only from a few scattered sites between North Cape and Dargaville. On the Chatham Islands it has turned up on Chatham Island in swamp forest near Waitangi West and on Pitt Island within swamp forest bordering streams draining into Lake Tupangi.
The second tropical moss is Pyrrhobryum paramattense which as the
species name implies is most common in eastern Australia. However, it extends
across onto Lord Howe, Norfolk
and the Kermadec Islands (Raoul only), and was discovered
in the far north of New
Zealand in the 1980s. It is now known also
from Chatham Island where it has been found once in
the Tuku Nature Reserve.
Naturalised mosses on the Chathams.
Only six mosses can be confidently
considered naturalised on the Chathams. The designation of a particular moss as naturalised
or indigenous is typically a matter of judgement by a taxonomist or ecologist;
it is based on many factors concerning a plant's ecological "behaviour", its
global and regional distributions, its regional collection history, and several
other considerations. In a few instances
(and in other parts of the world) modern molecular techniques have been used to
attempt to "prove" the introduced status of moss populations.
Of the five Chathams "certain" introductions, Eurhynchium praelongum is the most widespread and conspicuous. As on the main
islands of New Zealand,
E. praelongum is widespread on the Chathams in a range of disturbed sites
including lawns, fallow areas, soil and gravel areas at margins of tracks, and
on fallen logs. On the mainland of New Zealand it
forms wefts of several metres square under favourable conditions. Eradication, or even control, of this species
on the Chathams
is not feasible.
Fissidens
taxifolius is another well-documented naturalised
species on the Chathams. Although it is very widespread in the
northern hemisphere, it was first recognised in New Zealand about 60 years
ago. In the context of the genus it is
well marked and relatively large species, with distinctive dark green, rigidly
erect, feathery foliage. The leaf mid
rib characteristically reaches the acute leaf apex or very slightly beyond the
apex. This species does not produce
capsules in New Zealand
and the plants spread vegetatively. In ideal conditions they form dense tufts
within lawns, along track sides and stream banks. On the Chatham
Islands F. taxifolius has so far been recorded from a single site at Te One, where Department of
Conservation staff have attempted its eradication. Fissidens taxifolius is easily spread in garden waste and soil, and
it is likely that it arrived on the Chatham Islands
in soil attached to garden plants.
Other adventive mosses recorded from the Chathams include the less
well-documented Barbula unguiculata, B.
convoluta, Bryum cf. radiculosum and
Pseudoscleropodium purum. None
of these species are considered to pose a threat to indigenous vegetation. Other species, such as Amblystegium serpens, Brachythecium rutabulum, Bryum argenteum,
Bryum dichotomum, Funaria hygrometrica, and Fissidens adianthoides could possibly be introductions or occur on
the islands as both indigenous and introduced populations. Such differentiated populations would be
difficult to demonstrate and of little practical significance.
Conclusions
Mosses are an important part of the Chatham Island vegetation. As a result of
deliberate efforts to collect and study these tiny plants we now have a very
good understanding of the moss diversity on the islands. With nearly 200 mosses
now recorded, the Chatham Islands has about
one third of the estimated total number of mosses known from the New Zealand
Botanical Region. Notably despite its isolation and latitude, the islands' moss
flora supports a distinctive northern New Zealand tropical and southern New Zealand
element. The islands are also home to a number of threatened mosses.
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Encalyptra rhaptocarpa
Fissidens integerrimus
Fissidens berteroi
Calymperes tenerum
Ectropothecium sandwichense
Pyrrhobryum paramattense
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