Until the close of the last century very little was known and next to nothing published about the mosses of the Chatham Islands. Although the first moss gatherings were made by Henry Travers in the 1860's it was not until 1997 that Landcare Research staff visited the islands to specifically study mosses and liverworts. Since then, partly to assist with the preparation of upcoming New Zealand Flora treatments on bryophytes, mosses and liverworts have also been gathered from Chatham Islands by scientists from of the National Institute of Atmospheric Research and Department of Conservation. From these aggregated collections we now have a reasonable idea of the Chatham Island moss flora.
Currently c.199 different mosses have been recorded from the Chatham Islands. Only one, Macromitrium ramsayae is endemic. A small number, perhaps six species, are naturalised and the remainder are indigenous to New Zealand, Australasia or the wider Pacific. Of these mosses the majority are widespread species found throughout the main islands of New Zealand.
However, a small number follow a pattern already evident with the islands flowering plants and ferns, which is that some mosses previously only known from northern and southern New Zealand, are now known to occur on the Chatham Islands.
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.
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.