Pig fern
Botanical name: Hypolepis ambigua
Synonyms: Hypolepis tenuifolia sensu Hook.f., Polypodium amplum, Cheilanthes ambigua, Hypolepis petrieana, Hypolepis punctata sensu Dobbie
Common name(s): Pig fern
About:
A large, fast-spreading endemic fern of disturbed ground, forest margins and open country. Hypolepis ambigua produces broad, finely divided fronds from long-creeping rhizomes and can form extensive colonies where conditions are favourable.
The fronds are light green and generally three to four times divided, with scattered pale brown or colourless bristly hairs on the stalks, veins and lower frond surfaces. It is an opportunistic species and readily colonises disturbed soil, roadsides, clearings and open grassland, sometimes becoming locally weedy.
Natural habitat:
Coastal to montane.
Common in open forest, forest clearings, forest margins, scrub, grassland, river banks, alluvial flats, roadsides, tracksides, drainage ditches, sandy soils, margins of lakes, swamps and peat bogs, and around thermally heated streams.
It is particularly associated with disturbed ground and may also grow amongst bracken or beneath introduced conifer plantations.
Growing environment:
Sun, Partial Shade, Moist Soil, Disturbed Ground & Wind tolerant. Adaptable and vigorous once established.
Endemic distribution:
Endemic to New Zealand.
Found on Manawatāwhi / Three Kings Islands, the North Island, South Island, Stewart Island/Rakiura and Chatham Islands.
Height:
Fronds commonly 20 cm–1.8 m long, occasionally considerably larger.
Width:
Individual fronds may exceed 1 m wide.
Colonies can spread extensively by long-creeping rhizomes.
Flowering:
Not applicable — fern species reproducing by spores.
Fruiting:
Not applicable — spore producing.
Sori develop along the margins of the ultimate frond segments.
Uses:
• Native revegetation of disturbed sites
• Informal fern gardens
• Large-scale naturalistic planting
• Forest-edge restoration
• Colonisation of banks and open ground
• Habitat planting where vigorous spread is acceptable
Appearance:
Growth habit:
A robust terrestrial fern spreading by long-creeping rhizomes approximately 2–4 mm in diameter.
Fronds arise at intervals along the rhizome and may form large loose or dense colonies.
Leaves:
Fronds are broadly ovate to ovate in outline and typically deeply divided two to four times.
The lamina may reach approximately 1.2 m long and 1.2 m wide, although much larger fronds occasionally occur.
Primary pinnae are numerous, with the longest generally near the base of the frond. Lower pinnae arise at relatively narrow angles, while upper pinnae spread more widely.
Secondary and tertiary pinnae become progressively smaller toward their tips.
Ultimate segments are broader than those of some related Hypolepis species.
The lower frond surface carries conspicuous glistening colourless hairs, especially along the veins and midribs. Pale brown hairs occur on the rachis and stipe.
Glandular hairs are normally absent.
Flowers:
None.
As a fern, Hypolepis ambigua does not produce flowers or seeds.
Fruit:
None.
Spores are produced in rounded sori on the lower surface near the margins of the ultimate frond segments.
Each sorus is only partly protected by a slightly reflexed flap of the frond margin rather than a strongly developed indusium.
Spores are pale brown and finely echinate.
Ecology:
Hypolepis ambigua is an opportunistic coloniser strongly associated with disturbance.
Its rapidly spreading rhizomes enable it to occupy newly opened ground following clearing, erosion, fire, track construction or other disturbance.
The species can form extensive fern colonies and is often associated with bracken in open country.
Minute spores are dispersed by wind, allowing rapid colonisation of suitable newly disturbed sites.
It hybridises with several other New Zealand Hypolepis species where their distributions overlap, including H. dicksonioides, H. lactea, H. millefolium and H. rufobarbata.
Associated habitats:
Open forest, regenerating forest, forest margins, scrub, brackenfield, grassland, river terraces, alluvial flats, roadsides, tracks, drainage channels, lake margins, swamp margins, peat bogs, rotten logs and geothermal areas.
How to grow:
Very easy to grow but should be planted with caution because of its vigorous spreading habit.
It tolerates a wide range of soils and light levels but performs best in moist, reasonably fertile ground in full sun to partial shade.
Allow plenty of space for the creeping rhizomes.
In small gardens it may become invasive and difficult to contain, so it is better suited to larger naturalistic areas or restoration sites where rapid ground colonisation is desirable.
Propagation:
Easily propagated from fresh spores.
Spores can be sown on a moist, sterile fern medium and kept humid until young sporophytes develop.
Established colonies can also be divided by lifting sections of rhizome carrying healthy fronds and roots.
Because rhizomes spread quickly, only small pieces are normally required to establish new plants.
Cultural use:
No specific traditional Māori use is widely documented for Hypolepis ambigua.
The name Hypolepis derives from Greek words meaning “under” and “scale”, referring to the position of the sori.
The specific epithet ambigua means ambiguous or uncertain, reflecting historical taxonomic confusion surrounding the species.
Garden value:
A bold, vigorous native fern best suited to larger gardens, revegetation sites and informal native landscapes.
Its large, finely divided light-green fronds create a lush fernland effect and establish quickly in disturbed areas.
However, its strong rhizomatous growth means it can become troublesome in confined garden beds, so it should be used where its natural spreading habit can be accommodated.