Ring fern

Scientific name: Paesia scaberula
  • Key characteristics
  • Biology
  • Impacts
  • Control
  • Further information

  • Ring fern is a fern, producing spores not seeds, which is native to New Zealand
  • It spreads by means of underground stems (rhizomes) that send up leaves at intervals
  • It is a low-growing fern (usually up to 50 cm tall, sometimes taller) that forms extensive, dense patches in scrub or grassland
  • Rhizomes are stiff, 1-2 mm thick, and covered in slender dark brown hairs
  • Stipes (leaf stalks) are 10-30 cm long, and densely hairy at the base
  • The main axis of the leaf zig-zags strongly or sometimes only slightly
  • Fronds (leaves) are yellow-green, 15-45 cm long and 5-20 cm across, divided two or three times into small segments, giving the whole frond a ferny appearance. The frond unrolls as it grows
  • Spore-bearing organs (sporangia) are numerous on the underside margins of the leaf segments
  • Its common name arises from the characteristic ‘ring’ shape of each plant cluster
  • There are some similarities between ring fern and bracken.

Origin

  • It is native to New Zealand. Paesia scaberula has not naturalised overseas but is available from garden centres in the United States and the United Kingdom, under the name ‘lacy fern’ or ‘scented fern’
  • It is also found throughout New Zealand especially in rough hill pastures, wasteland and roadsides and in open places in forests. Like bracken it can be an aggressive invader after clearance of forest cover.

Life cycle

  • It is a fern, reproducing by spores that germinate to produce a small prothallus. This develops male and female sexual organs that in turn produce male and female gametes, resulting in the formation of a new fern plant.

Impact on farming

  • Ring fern can make stock access and mustering very difficult.

Impact on pasture

  • Ring fern, like bracken, can form very dense cover, smothering useful pasture species
  • It uses valuable soil nutrients for growth and these nutrients are locked up in the fronds until they eventually break down.

  • Ring fern is rhizomatous and difficult to kill
  • It commonly grows in poorer grazing land, therefore, its control may not be economically feasible.

Grazing

  • Grazing is not an effective method of control, but heavy treading by cattle can be used to crush the new fern shoots as they are emerging.

Mowing

  • Repeated mowing or crushing can be used as control measures. However, where ring fern grows on steep hillsides this may not be practical.

Pasture species/cultivars

  • Establishment of new competitive pasture species, suited to local conditions, can be used after initial clearance of fern and may, if adequately limed and fertilised, help to prevent reestablishment.

Forestry

  • Trees can form a dense canopy and shade out both species of fern but the trees must be protected from the ferns when young.

Chemical control

  • Glyphosate can be used for control of ring fern.

Biocontrol

  • No biological control agents are available for ring fern.

  • Popay I, Champion P, James T 2010. An illustrated guide to common weeds of New Zealand. New Zealand Plant Protection Society, Christchurch, New Zealand. 416 p.
  • Young S 2013. New Zealand Novachem Agrichemical Manual. Agrimedia Ltd, Christchurch, New Zealand. 767 p.