Pteridium esculentum (Forster f.) Cockayne
Synonyms - Pteridium aquilinum, Pteridium aquilinum var. esculentum, Pteridium aquilinum var. lanuginosum, Pteridium revolutum, Pteridium yarrabense, Pteris esculetna.
Some authors consider there is one world wide species of Bracken, Pteridium aquilinum, with many subspecies and varieties.
Pteridium is from the Greek pteris meaning fern.
Esculentum is from esculentus meaning edible because the Maoris ate the rhizomes.
Other names:Bracken Fern
Summary:A large, dark green, vigorous, leathery and invading fern with 'Christmas tree' shaped fronds.
Leaves:Fronds arising from underground rhizomes.
Long, stiff, leathery, erect, up to 2500 mm long including stalk. Frond held almost horizontally to the stalk.
Petiole - Stipe, erect, rigid, 100-1500 mm long, smooth, unbranched, initially covered with fine pale brown hairs and become hairless with age.
Blade - Initially light green becoming dark green to brown with age, shiny or dull, darker on the upper surface than the lower surface. Triangular in outline, finely divided 3 or 4 times in the lower part into parallel sided, narrow lobes that alternate on the stalk. Soft initially then becoming leathery and rigid. Hairless or sparse, short, reddish hairs on the upper surface especially near the edges. Low lying, white, fine hairs on the under surface. Edges of lobes rolled under to hold a line of brown spores. Circular nectary at the base of most minor lobes. Fronds on unbranched stalks (stipes).
Stems: Under ground rhizome.
Flowers: None. It produces spores.
Fruit:Fruiting bodies (Sori)
Difficult to see. Parallel sided, running along the margins of the minor lobes and enclosed by the rolled leaf edge.
Seeds:Spores. Usually only germinate and establish in old fire heaps.
Roots:Long, creeping, underground rhizomes covered with black scales and fine pale brown hairs. 5-20 mm thick.
Key Characters:Non arborescent fern.
Fronds compound, triangular, leathery, ultimate segments 2 mm broad.
Rhizome long, creeping, usually hairy.
Spores of one type.
Sporangia in groups, borne on the under surface of leaves, protected by modified leaf margin.
Sorus marginal, terminal on free veins.
Indusium opening towards the costa.
Adapted from J.M. Black
Perennial. Spores germinate in ash beds and complete the sexual portion of their life. Asexual ferns form and produce patches. Shading or allelopathy (the production of toxins) usually eliminates other plants within the patches. New fronds emerge from underground rhizomes in spring, and mature over summer. These fronds die in winter (usually after frost) and fall, smothering other plants. Patches spread about 1 m per year.
By spores, rhizome extension and rhizome fragments.
Flowering times:Seed Biology and Germination:
Allelopathy:Produces toxins that retard the growth and germination of other species.
Population Dynamics and Dispersal:Occurs naturally at low density in eucalypt forests but increases rapidly after clearing.
Origin and History:Australia, New Zealand.
Distribution:NSW, QLD, SA, TAS, VIC, WA.
Widespread in higher rainfall areas.
Courtesy Australia's Virtual Herbarium.
Temperate. Higher rainfall areas.
Soil:Sandy or well drained soils.
Used for Aboriginal and Maori food, bedding, thatch, medicines and gums.
Detrimental:Serious weed of pastures.
Weed of pastures, roadsides, disturbed areas, watercourses, recreational areas.
Toxicity:Toxic to sheep, pigs, people and especially horses and cattle when eaten in large quantities. Green fronds are most toxic, but dead fronds and rhizomes are also toxic. Hay containing Bracken can be toxic.
In WA, many cases attributed to Bracken Poisoning are probably due haemorrhagic septicaemia caused by the Pasteurella organism which induces very similar symptoms in young cattle plus diarrhoea and can be prevented by vaccination.
Bracken has 5 toxic principles;
1) Thiaminase. Causes Bracken Staggers in horses and Bracken Rhizome Poisoning in pigs. It is most prevalent in rhizomes and young fronds. It induces staggers, nervous and muscular disorders.
2) Bone Marrow Toxin. Causes Bracken Poisoning in cattle and occasionally sheep by interfering with bone marrow function. It causes cancers, birth defects, haemorrhages and high body temperature.
3) Bright Blindness Toxin. Associated with Bone Marrow Toxin.
4) Shikimic acid. Produces tumours of the bladder and gut of sheep and cattle grazing small amounts of bracken for long periods. A carcinogen can be passed in milk and urine.
5) Prunasin. Toxic but not reported as a field problem because animals probably don't eat plants that have high levels.
Induces vitamin B1 deficiency and haemorrhaging in cattle.
Symptoms:May take days or weeks to show even if stock have been removed from the infestation.
Cattle get 3 types of disease;
1) Enteric type; dullness, fever, loss of appetite, blood stained urine and faeces, bleeding from natural openings and skin, death.
2) Laryngitic type; mainly in claves, dullness, discharge from nostrils and mouth, swollen throat, difficulty breathing, fever, death.
3) Bladder cancer.
Horses show staggering, standing with the feet well spread and an arched back, severe muscular tremors, collapse and struggling, convulsive seizures, tetanic spasms and death.
Sheep are generally not affected but may show bright blindness due to degradation of the retina or excessive bleeding after castration or mulesing.
Pigs may show dullness, lack of appetite, lying down, difficulty breathing and death due to heart failure. It usually occurs where pigs are used to clean up bracken patches by trampling and digging for rhizomes.
Humans and especially children have a greater incidence of stomach cancer in areas where freshly cooked or canned bracken shoots are eaten or milk from bracken fed cows is regularly consumed.
Treatment:Don't force animals to consume large amounts of bracken or small amounts over long periods. Avoid over grazing, provide supplementary feed in summer and roughage in winter.
Horses and pigs can be treated with thiamine injections, thiamine rich rations or supplements containing vitamin B1.
Cattle and sheep can be given antibiotics and blood transfusions.
Legislation:The Wildlife Conservation Act prohibits the removal of this species from natural stands on government land.
Management and Control:Consistent, repeated slashing, mowing or rolling provides reasonable control but is expensive. Repeated cultivation also provides some control but many of the soils where bracken occurs are too fragile for this treatment. Fertilising to encourage pasture species and grazing reduces the density and spread. Glyphosate and metsulfuron provide high levels of control. Metsulfuron is more cost effective. Establishment of suitable pastures or revegetation reduces reinvasion.
Burning is useful for removing dead frond material to reduce toxic effects before replanting pasture. Burning by itself usually leads to an increased infestation.
Pigs are sometimes used on small patches to trample the fronds and root out the rhizomes. They should be fed a vitamin B1 supplement to reduce the risk of poisoning.
Slash heavy stands in winter.
Apply Brush Off at 60 g/ha in early summer when fronds have fully unfurled. Apply again in autumn if necessary. Control annual weeds with glyphosate 450g/L at 2 L/ha after the break of the season. Cultivate 10 days later. Plant competitive and preferably perennial pasture species. Control remaining fronds in summer, after rain, using a mixture of 10 g of Brush Off per litre of water applied with a wick applicator or blanket wiper.
Herbicide resistance:Biological Control:
Plants of similar appearance:Ferns.
References:Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P3, 13. Photos.
Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P61. Diagram.
Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P28. Photo.
Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P775-781.
Gardner, G.A. and Bennetts, H.W. (1956). The toxic plants of Western Australia. (West Australian Newspapers Ltd, Perth). P3-5.
Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P12. Photo.
Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).
Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #1033.1.
Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P51.
McBarron, E.J. (1983). Poisonous plants. (Inkata Press, Melbourne). P25-26. Diagram.
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