Most mosses are small, green leafy plants attached to soil, bark or rock by fine filaments known as rhizoids. Some have single erect stems, whereas others have branching stems and develop into a sprawling carpet or drape from trees. New Zealand’s tallest moss, Dawsonia superba, grows to a height of half a metre, but few others are anywhere near that tall – most are about 1–2 centimetres tall.
The moss life cycle has two different plants. One of those two plants produces spores, and in mosses it’s always attached to and partially dependent on the other plant, which produces sex cells.
Mosses occupy a wide range of habitats in New Zealand. Many favour damp, shady sites, and thrive on the forest floor and around the base of trees. Others flourish best in light, and grow as epiphytes on the branches of trees, or in open areas such as clay banks and the edges of tracks. A few are aquatic, submerged in streams and lakes. All sphagnum or peat mosses grow in swamps and bogs where there is standing water year-round. Granite mosses (Andreaea species) are a hardy group and form dense, dark cushions on alpine rocks.
In the city, few plants can take root in concrete and bitumen, and even fewer can cope with the petrochemicals and dust in the air. But half a dozen moss species can grow far better in the cracks and crevices in footpaths, walls, gutters and drains than they ever could in the bush. They are called urban mosses. One in particular, the silvery bryum (Bryum argenteum), has established itself in cities everywhere, and is now the most widespread plant in the world.
Silvery bryum looks silvery because the cells of the upper third of its leaves die and lose their chlorophyll. Their skeletal remains are white and shiny, especially when dry. The dead tips act like a layer of sunscreen, protecting the still-living lower two-thirds of the leaves from damage by ultraviolet radiation. When the dead leaf tips are dampened by rain, they turn glass-like, allowing light to penetrate the moss cushion.
Many mosses have some things in common with the stalwart silvery bryum. They are small and can fit into cracks and knotholes, where bigger plants cannot survive. They do not die if they dry out, and do not suffer if their habitat becomes dry, or if wet and dry conditions alternate. During dry spells their metabolism shuts down until the rains return, when their processes are re-launched and repairs are quickly made. Large plants cannot do that, because drying fatally airlocks the complex internal pipes that carry water and dissolved minerals and food.
There are three different types of mosses:
The true mosses (with over 500 species) make up 95% of all New Zealand mosses. New Zealand has nine species of sphagnum. The granite mosses are rarest, with five species.
New Zealand boasts some 550 species of moss in more than 200 genera – a rich variety for such a small area. Only about one-fifth are endemic – meaning they are found nowhere else. In comparison, four-fifths of the country’s flowering plants are endemic. There are relatively fewer endemic mosses because their lightweight spores are dispersed far and wide by the wind. As well, new plants can sprout from even tiny fragments carried on the feet and feathers of migrating birds.
Some endemic species are peculiar enough to entice botanists from around the world. Among them is Epipterygium opararense, known only from individual stems growing on a boulder in the Kahurangi National Park, in the north-west of the South Island.
The world’s most valuable moss is peat moss (Sphagnum species). One per cent of the earth’s land surface – half the area of Australia – is peat bog. Sphagnum is harvested for fuel, garden mulch and packaging. In New Zealand, sphagnum is harvested from Westland and Southland swamps for export as a horticultural growing medium. Most is sent to Japan, where it is used for growing orchids. However, peat moss is most valuable as a colossal carbon sink – it stores 400 billion tonnes of carbon (14% of the world’s total), which could otherwise be converted to atmospheric carbon dioxide, which is a greenhouse gas and worsens global warming.
Two New Zealand mosses, Campylopus introflexus and Orthodontium lineare, were accidentally introduced into Europe, where they have become noxious weeds, spreading quickly and displacing native mosses. Campylopus smothers the ground so completely that it interferes with the germination of seeds of trees and shrubs.
Two other moss exports are Calomnion complanatum and Leptotheca gaudichaudii.These are not a threat.
At least 14 species of moss are recent introductions to New Zealand. Rhytidiadelphus squarrosus was first recorded in the 1970s, and has become common along roadsides in the South Island. A related northern hemisphere species, shaggy moss (R. triquetrus), grows in scrub at Nelson Lakes, and has the potential to establish itself in the nearby National Park.
Māori decorated and insulated some of their traditional flax garments with two species of hair-cap moss, Polytrichum commune and Polytrichadelphus magellanicus. The flax strands were woven so tightly that the moss could not be poked in as an afterthought, but had to be carefully inserted during weaving.
Beever, J., and others. The mosses of New Zealand. 2nd ed. Dunedin: University of Otago Press, 1992.
Fife, A. J. ‘Checklist of the mosses of New Zealand.’ Bryologist 98 (1995): 313–337.
Malcolm, Bill, and Nancy Malcolm. The forest carpet. Nelson: Craig Potton, 1989.
Sainsbury, G .O. K. A handbook of the New Zealand mosses. Wellington: Royal Society of New Zealand, 1955.