Friday, November 4, 2011

New Zealand: Fascinating Fernery

On the way back from Punakaiki (see previous post), Kerry-Jayne stopped at the Pororari River Track (in Paparoa National Park) to show me a unique, if unspectacular, plant. The Pororari winds through a spectacular forested gorge on New Zealand's west coast, emptying into the sea at Punakaiki itself. The lush and humid forest along the track is particularly rich in ferns, and it was a fern - of sorts - that we had come to see.

New Zealand is particularly rich in ferns and the plants usually called "fern allies", though how closely related some of them actually are to ferns is open to question.

Many of Pororari's ferns grow epiphytically - that is, on the trunks and limbs of trees. This one appears to be Microsorum scandens, a fern that features strap-like, undivided juvenile fronds and deeply-lobed adult fronds in the same clump. The species is well-named: scandens means "climbing".

Here is the plant we were looking for - not much to look at, but I was very excited to see it. It is Tmesipteris elongata, and when I studied botany as an undergraduate it was regarded as one of the most primitive plants in the world. Tmesipteris, the fork fern, and it's only relative, Psilotum, the whisk fern - the so-called whisk fern - were thought to be living representatives of the very first green plants to invade the land. Like these early plants, Tmesipteris and Psilotum have neither roots nor leaves (the little structures that look like leaves on Tmesipteris, put simply, aren't. They lack vascular tissue, the vessels that provide both support and transport in higher plants). What is more, they carry their packets of spores (sporangia, the little green blobs that look vaguely like miniature olives) out in the open, as the earliest plants did (though not, as it happens, in the same way).

Unfortunately for this lovely idea, it appears that Tmesipteris and Psilotum are simply ferns that have somehow lost their more advanced features. Modern molecular studies place them close to the adder's tongue ferns (Ophioglossaceae). Oh well... I was still excited to find this little fellow, growing unobtrusively among less celebrated plants.

Here is an epiphytic plant that is neither a fern nor a fern ally, but a liverwort - don't ask me which one! Liverworts are not vascular plants, but are closer to mosses.

This is unquestionably a fern, and to my eye it is one of the most unusual and striking of them all. I first saw kidney fern (Trichomanes reniforme) in 1974, on Little Barrier Island. I was struck by it then, and was delighted to see it again so many years later.

The kidney fern belongs to the filmy fern family (Hymenophyllaceae). It doesn't look too much like other filmy ferns, but it share with them extremely thin fronds, only a few cell layers thick, that dry out very easily. Kidney ferns can survive drying, shriveling and then reopening when the rains come, but their presence is a sign that the forests where they grow are, at least some of the time, humid places indeed. The little blobs around the rim of this fertile frond are the spore-bearing bodies, or sori.

Here are some more traditional ferns.I'm not sure what the upper plant is, but the lower one appears to be crown fern or petipeti (Blechnum discolor).

I believe this to be one of the many New Zealand species of Coprosma - possibly karamu (C. robusta), but there are some fifty to choose from.  We have Captain Cook's botanists to thank for the unlovely generic name, from the Latin copros, meaning dung.  Apparently the specimens they collected stank up their shipboard cabins.

This is a Dracophyllum,one of the plants that gives New Zealand forests - at least to a northerner's eye - a distinctly exotic appearance.  Though it doesn't look it, it is a relative of heathers and heaths (Ericaceae), as one of the plants formerly included in a separate, largely southern-hemisphere family, Epacridaceae.

In most parts of the world, if you found one tree busily engaged in trying to choke the life out of another, you would be safe in assuming that the murderer in question was a strangler fig. In New Zealand, though, it is more likely to be a northern rata (Metrosideros robusta), a member of the myrtle family (Myrtaceae). While other ratas (and other Metrosideros spp., like the famous ohia lehua (M. polymorpha) of Hawaii) usually grow from the ground up like respectable trees, the northern rata starts life as an epiphyte high in the canopy. In time, like a strangler fig, its roots reach to the ground, forming a robust pseudotrunk that envelops and, eventually, smothers its host (though there is some argument as to whether the rata actually contributes to the death of the host tree).

The result can be a truly impressive tree, reaching 25 m in height. This one, it seems is well on its way.

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