Chris Horne of the Wellington Botanical Society recently sent me a fern frond they collected on one of their trips. Although the frond is small and lacking the diagnostic reproductive characters, I think it is the introduced holly fern (Cyrtomium falcatum). It looks like the shining spleenwort (Asplenium oblongifolium), but the flanges, or ‘teeth’, of the frond segments are distinctive (amongst ferns in New Zealand).
Holly fern and shining spleenwort can be readily distinguished when mature. The reproductive structures of the holly fern resemble those of the shield ferns (Polystichum), to which it is related, while the shining spleenwort has typical spleenwort reproductive structures.
Holly fern is native to Asia, but it is sporadically cultivated in New Zealand, and it has become weedy in several parts of the country. Steve Benham wrote an article for the Auckland Botanical Society Journal (v.63 (1), pp.25-27) suggesting gardeners should be dissuaded from cultivating holly fern in the Northland and Auckland regions, because of its invasiveness in that part of the country.
It is certainly a fern that should be monitored, so it would be good to get reports of holly fern growing wild.
Two other weedy ferns to keep an eye out for are common polypody, Polypodium vulgare, and the male fern, Dryopteris filix-mas.
The common polypody, from Europe and Asia, is a common weed on Banks Peninsula, and it has recently been found in Wellington (near Plimmerton) and Marlborough (near Kaikoura and near Hanmer Springs).
It looks like the native hound’s tongue, Microsorum pustulatum, but can be distinguished by its frond being dissected right to the stem of the frond. Polypodium vulgare can be a terrible, smothering weed, so it is important that it is stopped from spreading further. Regional Councils should be notified of any additional localities.
The male fern, Dryopteris filix-mas, is also from Europe, and has established in many parts of New Zealand. I have been amazed at how widespread it is in the South Island, but I haven’t collected it as often as I should have, and Te Papa’s collections don’t do its invasiveness justice. Male fern is unusual in that it can invade relatively intact native forest, making it a formidable weed. A very similar species, Dryopteris affinis, is also weedy in New Zealand.
I would be interested in reports of these species and other introduced ferns growing wild in New Zealand. This will help us better understand their invasiveness. Please contact me at firstname.lastname@example.org, or 04 381 7261, or Leon Perrie, Te Papa, PO Box 467, Wellington.