Numbers of species
Although ferns and lycophytes are a conspicuous feature of New Zealand’s vegetation, the country is not as richly endowed in species as many other places. New Zealand has 194 native species and 35 that have been deliberately or accidentally introduced and have become established in the wild. This is a tiny fraction of the 12,000 known species worldwide, but is fairly typical of temperate floras. Rich fern floras are found in tropical countries. New Zealand’s tropical neighbours Fiji and New Caledonia, each with a land mass one-fourteenth the size of New Zealand’s, have 250 or more fern and lycophyte species.
Largest fern families
Many distinctive fern families are found in New Zealand. They include species that range from tiny ferns a few millimetres long to 20-metre-tall tree ferns.
With 27 species, filmy ferns (genera Hymenophyllum and Trichomanes) form the largest fern family in New Zealand. They thrive in humid forests – their translucent fronds, just one or two cells thick, lose water easily and curl up in dry conditions. Some, such as the kidney fern or raurenga (Cardiomanes reniforme), grow on the forest floor, while others are epiphytic on the trunks of trees and tree ferns. Hymenophyllum malingii is one of the most unusual in this respect, as it is usually only found growing on dead trunks of kaikawaka (Libocedrus bidwillii).
Hard ferns (Blechnum) are the next largest group, with 23 species. They have two types of frond. Sterile fronds are green and leafy, while fertile fronds have very narrow segments bearing copious brown, spore-bearing capsules (sporangia). Some species develop red or pink fronds when growing in the open.
New Zealand has 18 species of spleenwort (Asplenium), so named because they were thought to cure diseased spleens. They are readily recognised by the herringbone arrangement of sori on the undersides of the fronds.
Tree ferns have a thickened, vertical stem topped with an umbrella-like crown of fronds. They can be found throughout the country, in the bush and along its margins, as well as standing in groves in pasture. Eight species grow in mainland New Zealand, and two (Cyathea milnei and C. kermadecensis) are only known from the Kermadec Islands, north of New Zealand.
Whekī (Dicksonia squarrosa) is probably the most common tree fern, often found in groves in damp lowland forest. It is a hardy plant and will re-sprout from underground stems after fire or bush clearance. Mamaku (Cyathea medullaris) and gully fern (C. cunninghamii) are the tallest, growing to over 20 metres. Silver fern or ponga (C. dealbata) is readily distinguished by the white underside to its frond. Soft tree fern (C. smithii) is the world’s southernmost tree fern, growing on the Auckland Islands at 50˚ south. It is recognised by its skirt of dead fronds around the trunk.