Ferns and Fern Allies in the Canberra Region

Polystichum proliferum - Mother Shield Fern

Polystichum proliferum is a very hardy ground fern that is widespread on the mountainsides to the west of Canberra. It colonises wide areas both by propagating via proliferous tips at the end of its fronds, and by spores. It is often assoicated with Dicksonia tree fern gullies, growing higher up the slopes, further away from the watercourse than the tree ferns. It grows from a central rhizome, with fronds up to a metre (3') in length. Its fronds are usually a dull darkish green. With age the fern may develop a trunk-like base. To the untutored eye, a large P. proliferum can look like a young tree fern.

There are several varieties of Polystichum in Australia but it is not at all clear that all species have been fully identified or described. Polystichum australiense has also be tentatively identified from the Canberra region.

P. proliferum is so named because of the proliferous buds it grows on its fronds. These start as a bud and grow into a small plant, towards the end of the frond, before the frond sags to the ground and the new plant takes root. The image to the right shows a young proliferous bud.

The pinnae of most specimens of P. proliferum in the Canberra region look like the image at right. Note the groove running along the stipe (frond stalk) and the brown scales. Some specimens, however, show a distinctly different appearance. These have tended to be clumped into the same species, but this is something that needs to be checked carefully.

One plant we found in the Blue Range, growing under a waterfall (not the usual place for P.proliferum) was distinctly different, both in the shape of the pinnae and the black hair-like scales on the base of the rhachis (stalk). At a distance, too, there was something quite "different" about its appearance, which attracted our attention. Compare this image with the one above to see how the pinnae of the two specimens differ. The photos are of plants collected within a few metres of each other. We intend to look for more specimens of the "new" variety.

The veination of the pinnae, and especially the way in which the pinnae are attached to the stipe, are quite distinctive. The image at right, of the underside of the frond, shows this clearly. Taken together with the black hair-like scales, there's a good case for this being a new species. It is this sort of discovery that can make one's efforts really rewarding.

David Nicholls
July 1998