ARTICLE : Polypodium vulgare: A new weed fern for Wellington

 Polypodium vulgare: A new weed fern for Wellington

Figure 1.   Frond (c. 20 cm long) of Polypodium vulgare from Hongoeka Bay, with the frond’s primary pinnae dissected right to the rachis.

We recently found a naturalised population of the fern Polypodium vulgare (Figures 1 and 2) at the north-western end of Hongoeka Bay (Te Rewarewa Point), while walking the coastal track between Plimmerton and Pukerua Bay.   In New Zealand this fern is otherwise known to be established in the wild only on the Port Hills near Christchurch, where it is now a bad weed.

Polypodium belongs to the family Polypodiaceae.   No Polypodium species are native to New Zealand, but we do have indigenous Polypodiaceae species in the genera Microsorum, Pyrrosia, and Anarthropteris (Brownsey & Smith-Dodsworth, 2000).

Polypodium vulgare belongs to a polyploid species complex with P. cambricum (previously known as P. australe) and P. interjectum that is native to Europe and Asia.   These species look similar to each other, but can be distinguished with micro-morphological characters (number of indurated annulus cells, and the number of cells between the annulus and sporangial stalk; Page, 1997).   These characteristics confirm the specimens from Hongoeka Bay as P. vulgare.

We are unaware of Polypodium vulgare being a weed anywhere else in the world.   It was first recorded as naturalised in New Zealand on the Port Hills near Lyttelton during the 1960s and 1970s, but was probably present earlier (Lovis, 1980).   Lovis’s (1980) description of the distribution of P. vulgare on the Port Hills suggests it was rather localised at that time, but it is now widespread, occurring from Godley Head to Gebbies Pass, and is also on Quail Island (Hugh Wilson and David Glenny pers. comm.).   Hugh Wilson describes it as an “aggressive spreader” and probably a “lost cause” on the Port Hills.   No active control of P. vulgare on the Port Hills has been attempted, but it is being considered.   It has been noted that the gorse-killing herbicide Tordon is ineffective against P. vulgare (Di Carter pers. comm.).

Figure 2.   A fertile frond (c. 20 cm long) of Microsorum pustulatum from Hongoeka Bay, with the primary pinnae not dissected completely to the rachis.

Polypodium vulgare has a creeping rhizome but probably spreads mainly via its spores.   At Hongoeka Bay there are about 20 discrete patches of Polypodium vulgare, almost all less than c. 10m² in extent.   These occur along about 250m of the coastal hillside, bounded by the NZMS 260 coordinates E2664754, N6014033 to the east and E2664578, N6014177 to the west.   We saw P. vulgare only in open, grassy areas towards the bottom of the hillside, just above the vehicle track.   It was frequently growing with the native and morphologically similar Microsorum pustulatum.

Pest plant officers from Greater Wellington Regional Council have been notified.   The rocky cliffs and screes of much of the Wellington coastline are broadly similar to the Port Hills.   Left unchecked, Polypodium vulgare could become a widespread weed around Wellington.

Polypodium vulgare has been cultivated in New Zealand, but seemingly not to any great extent.   Both Van der Mast and Hobbs (1998) and the Auckland Botanic Gardens (1997) recommend planting Polypodium vulgare in New Zealand gardens, but we think this unwise given the proven invasiveness of this species in New Zealand.

Polypodium vulgare looks similar to our native Microsorum species, but it can easily be distinguished by the primary pinnae of its fronds being dissected right to the rachis (the main frond stem; see Figure 1).   In contrast, the rachis of Microsorum is winged throughout (Figure 3).   The rhizome of Polypodium vulgare seems to be partially buried, while that of Microsorum is largely above ground.

It is possible that Polypodium vulgare is already more widely established around Wellington.   We would be grateful for reports if people find it elsewhere.

We would like to thank Jeremy Rolfe for Figure 2; Barry Sneddon, Barbara Mitcalfe, Chris Horne, and Robert Quan for help with field observations; Hugh Wilson, David Glenny, and Di Carter for information about the Port Hills’ populations; and Pat Enright, Robyn Smith, Colin Ogle, Peter de Lange, Barbara Parris, and Patrick Brownsey for other information.

Lara Shepherd and Leon Perrie Te Papa, P.O. Box 467, Wellington.   Email : leonp (at) tepapa.govt.nz.   Phone 04 381 7261.

Figure 3.   Underside of a Polypodium vulgare frond, showing the round sori.   Photo: Jeremy Rolfe.

References

Auckland Botanic Gardens.   1997.   Ferns for Auckland.   Advisory leaflet B12.   www.aucklandbotanicgardens.co.nz > gardening > gardening techniques > advisory leaflets > bulbs and perennials

Brownsey, P.J., & J. Smith-Dodsworth.   2000.   New Zealand ferns and allied plants.   David Bateman Ltd., Auckland.

Klein, R.   2004.   Phytoecdysteroids.   Journal of the American Herbalists Guild, Fall / Winter 18-28.   www.rrreading.com/files/ecdysteroids_rklein

Lovis, J.   1980.   A puzzling Polypodium on the Port Hills.   Canterbury Botanical Society Journal 14: 55-57.

Page, C.N.   1997.   The ferns of Britain and Ireland.   2nd ed.   Cambridge University Press, Cambridge.

Van der Mast, S. & J. Hobbs.   1998.   Ferns for New Zealand Gardens.   Godwit Publishing Ltd., Auckland.