Overview
The fronds of tangle ferns are unusual in that their fronds repeatedly divide in two. They become entangled with one another and with other vegetation.
Tangle ferns in New Zealand usually occur in wet places such as swamps. They extend from coastal to alpine areas, but are largely absent from the drier east of both the North and South Islands.
They are classified in the genus Gleichenia. There are about 12 species worldwide. They occur in southern Africa and neighbouring islands, south-east Asia, New Guinea, Australia, New Caledonia, and New Zealand.
There are four species indigenous to New Zealand. One of these, Gleichenia inclusisora, was only discovered in 2010. It was first recognised from specimens in Te Papa’s collections.
- Gleichenia alpina (alpine tangle fern) occurs in alpine environments of the central North Island to Stewart Island, descending to sea level in the south of its distribution. It also occurs in Tasmania. It has shorter frond branches than the other New Zealand species, and a dense covering of scales that obscures the underside of its fronds.
- Gleichenia dicarpa (tangle fern, matua raruhe) is widespread in New Zealand (except for eastern districts), and also occurs in Australia, New Caledonia, and possibly south-east Asia. It is frequently found in swamps. The frond underside is white, and the segments are usually markedly pouched.
- Gleichenia inclusisora (pitted tangle fern) occurs in the western South Island, with an outlying population in northern Coromandel. It is only known from New Zealand. The frond underside is white and the segments are flat. Distinctively, the reproductive structures are sunk in pits rather than on the surface of the frond underside as in the other New Zealand species. This is the derivation of its scientific name, inclusisora being Latin for embedded fern reproductive structures.
- Gleichenia microphylla (carrier tangle, waewae-kotuku) is widespread in New Zealand (except for eastern districts), and also occurs in Australia. It seems more often to be on forest margins. The frond underside is green, and the segments are flat and not pouched. Despite its scientific name (which dates from 1810), Gleichenia microphylla has the largest frond segments of the species in New Zealand.
Gleichenia belongs to the same fern family as Sticherus and Dicranopteris. There are four species of Sticherus indigenous to New Zealand. Two of these are very uncommon, while Sticherus flabellatus is restricted to the northern North Island and Sticherus cunninghamii is widespread. The only species of Dicranopteris in New Zealand is restricted to geothermal areas of the central North Island.
Te Papa’s collections of Gleichenia tangle ferns in Collections Online.
Te Papa blog post about the discovery of Gleichenia inclusisora.
Te Papa blog post with more about the recently discovered Gleichenia inclusisora.
Reference:
Perrie LR, Shepherd LD, Brownsey PJ (2012) Gleichenia inclusisora, a new and uncommon tangle fern from New Zealand. New Zealand Journal of Botany 50: 401-410. Online abstract.