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Microsorum pustulatum
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This article was published in The Fringe, November 2015

Hound’s Tongue Fern or Paraharaha

In central Auckland you will find this rhizome-creeping fern in most of our parks growing high up on oak trees, while the inner suburbs such as Epsom have lots of it adorning the volcanic rock walls along with the smaller-leafed Pyrrosia eleagnifolia or leather-leaf fern.  Out west it is probably more common on the ground in the native bush areas, but if you haven’t swept the leaf litter from the carport roof you may well find a thick covering of rhizomes with their half metre fronds standing erectly.

The hound’s tongue name derives from the single broad blade that develops as the sterile juvenile frond. In times of drought it may well ‘flop’ rather like a hound’s tongue might do when the dog is thirsty. More commonly the leaves are larger and deeply dissected with deep lobes in opposite pairs. The more mature ones display the sori sunk into the leaf under-surface with a corresponding bump on the upper-surface. The sori are the cluster of sporangia from which the spores are released to begin the next generation of plants. They may look as though they are disfiguring the plant but the regular pattern dispels any thought of it being a disease.

Talking of disease, each year I catch people wandering into my driveway, snipping off pieces of the Microsorum I have planted along the edge. Apparently they find it is beneficial and use it medicinally as their forbears have done.  Throughout the Pacific there are related species of fern which were and still are used for a variety of illnesses.

Microsorum grossum, locally called metuapua'a, is one of the most frequently used fern species in Polynesian traditional medicine. Fronds or rhizomes of this species are common ingredients of popular medicine recipes to cure various ailments. M. grossum frond and rhizome extracts have been shown to have healing properties, particularly in protecting the skin from the harmful effects of too much exposure to sunlight.

Microsorum is not the first name this very confused plant was given. It has a long history of being pushed and shoved from one genus to another, and not content with that, the species name has changed almost as often. From Polypodium diversifolium to Polypodium billardieri, to Phymatodes  billardieri, to Micosorum diversifolium, to Phymatodes diversifolium, to Phymatosorus diversifolius and Phymatosorus pustulatum, to currently Microsorum pustulatum. That’s a name change every 25 to 30 years, so it is no wonder that we can all get confused by these ever changing names. But it all leads to the day where we have a defined species with a clear understanding of its natural distribution and relationship with other species. It is called progress.

However, the fern is oblivious to all the rules and name changes. Several years ago I had been doing some off-roading in my vehicle and perhaps did not clean it straight away. Now I can’t clean it, because a tender young Microsorum pustulatum has taken up residence in the body trim just below the driver’s door.  It takes months, if not years, for the wind-blown spore to develop into the ‘prothallus’ or sexual stage of a fern’s life-cycle. Then if fertilisation occurs, the young fern tentatively produces first a frond then a slow-moving rhizome. If it survives and there is sufficient nutrient for it, then it will produce a second slightly larger frond, perhaps 2 -3 mm long. I probably first saw the fern when it produced perhaps its fifth or sixth frond a centimetre long. Now it has fronds 3-5 cm long and it has survived some long distance travel, returning home looking decidedly wind-blasted. But each spring new fronds develop and it looks forward to new adventures with me as we go off-road searching for more exciting native plants.

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