Ferns have vascular tissues but lack seeds. They reproduce by spores. Together with lycophytes, they are unique amongst other living land plants in that the two phases of their life-cycle are both free-living. Ferns are generally distinguished from lycophytes by their big-leaved fronds ("megaphylls" rather than microphylls).
There are two main groups of ferns, based on the spore-producing structures. The leptosporangiate ferns form the bigger group and they include most of the typical fronded ferns, while the eusporangiate ferns include some rather odd plants. Some of the latter used to be grouped with the lycophytes as "fern allies", but they are actually more related to ferns.
About 200 species of fern are native to New Zealand. Almost half of these are also native to south-east Australia or elsewhere in the world. More than 30 exotic ferns have naturalised in New Zealand. There are about 10 000 species of fern in the world.