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Pteridium aquilinum (L.) Kuhn

Protologue
Cryptogamae vasculares. In: Decken, Reisen in Ost-Afrika 3(3): 11 (1879).
Family
Dennstaedtiaceae
Chromosome number
2n = 52, 104, 208
Synonyms
Pteris aquilina L. (1753), Pteris esculenta G.Forst. (1786), Pteris lanuginosa Bory ex Willd. (1810), Pteridium esculentum (G.Forst.) Nakai (1825).
Vernacular names
Bracken, brackenfern, eagle fern (En). Fougère-aigle, fougère grand-aigle, fougère des savanes (Fr). Feto ordinário, feto dos montes (Po). Mjimbi (Sw).
Origin and geographic distribution
Pteridium aquilinum is a cosmopolite and especially common in temperate zones. It is present on all continents, including Antarctica. It is one of the most widespread plant species of the world. In Africa it ranges from the Mediterranean to the Cape.
Uses
Pteridium aquilinum is widely used as a cooked vegetable. In the area around Bafoussam (Cameroon) it is reported to be consumed on a regular basis together with plants such as Vernonia amygdalina Delile and Triumfetta rhomboidea Jacq. In Gabon the young still enrolled fronds (croziers, fiddleheads) are reported to be edible. Several tribes in Angola eat the leaves. In Europe a number of accidents have happened with animals eating the leaves. Still, several sources mention its use as a vegetable in many countries, sometimes on a large scale. To render them edible, the croziers are soaked in water containing wood ashes for 24–36 hours to remove the free tannic acid. Up to the present the croziers are popular in Japan, where they are boiled, dried and stored for use in winter. Canned croziers are sold in Japan as ‘warabi’ or ‘zenmai’.
In Madagascar and the Canary Islands the rhizome is reported to be edible, in France they were used as feed for pigs. The rhizomes produce starch, which was used extensively by Canadian Indians in the past. In Japan, the starch is used to make confections.
The leaves are used as straw for cattle and as bedding. The leaves are also used to filter oil and palm wine. Dried powder of croziers is applied to old wounds. In Côte d’Ivoire the pulp of cooked croziers is used as enema to overcome sterility in women. The rhizome together with the rhizome of ginger (Zingiber officinale L.) is pounded and the juice is drunk as an aphrodisiac. As component of a mixture with 7 other ingredients it is used to calm the mentally disabled.
In China, water in which the leaves have been soaked is applied as a pesticide. The ash, having a high potash content, was formerly used extensively in Europe for glass and soap production. Bracken ash was particularly useful for making clear colourless glass. Wettened bracken ash was sold in balls to wash clothes and to bleach linen.
Properties
The whole plant of Pteridium aquilinum contains poisonous and antinutritional compounds. The compounds isolated include sesquiterpenoids (ptaquiloside and related substances, in general called pterosins, having insecticidal and carcinogenic activity), ecdysone (terpenoid compound, identical to the moulting hormone of insects), cyanogenic glycosides, tannins and phenolic acids. All these constituents may have some activity as a feeding deterrent. Shikimic acid has been found in all parts of bracken, especially in the rhizome. It has carcinogenic activity and may explain the occurrence of a fatal haemorrhagic syndrome in cattle and stomach cancer in humans after eating bracken foliage regularly. Bracken also contains an enzyme which destroys vitamin B1, resulting in vitamin B1 avitaminosis which causes brain damage in horses and other non-ruminants and acute enzootic haematuria (’redwater disease’) in cattle. The occurrence and concentrations of the various chemical constituents vary with the subspecies and varieties. The rhizomes appear to be about five times as toxic as the leaves. It is hard to detect and diagnose poisoning because of the delayed toxicity. Symptoms and death have developed as long as eight weeks after animals had ceased to eat the plants. The health hazard for humans is reported to be greatest for young children.
Botany
Terrestrial fern, with up to 2.5 m tall, finely divided leaves; rhizome long, creeping deep in the soil, repeatedly branched, covered with fine, pale brown hairs. Leaves appearing on short rhizome branches, never very close together; petiole thick, up to more than 1 m long, pale, in cross-section showing a horseshoe pattern of vascular bundles; lamina large, in outline ovate-triangular, up to 2 m × 1 m, 2–4-pinnate; all axes grooved on upper surface and often hairy; basal pair of pinnae usually subopposite, up to 70 cm × 40 cm, upper pinnae and pinnules gradually reduced and confluent; ultimate divisions pinnately compound or lobed, often with a long, entire, apical portion; segments oblong, obtuse, adnate, often with winged expansions at base, often interspersed with smaller and short lobes, margins entire, always revolute. Sori submarginal, linear, mostly continuous on marginal vein connecting the lateral vein ends; sporangia borne between the outer indusium consisting of the reflexed segment margin and the thin inner indusium. Spores trilete, tetrahedral-globose, 23–35 μm in diameter, irregularly granulate.
Pteridium aquilinum is a very variable species. Subsp. aquilinum is most common in Africa. Another subspecies, subsp. centrali-africanum Hieron. (synonym: Pteridium centrali-africanum (Hieron.) Alston), often regarded as a separate species, occurs from Gabon to Mozambique.
Ecology
Pteridium aquilinum grows along forest margins and the edges of thickets in savannas, where it may form dense populations of almost pure stands, and is often regarded a weed. It prefers altitudes of 750–2350 m.
Management
Because of its ability to form dense man-high populations, bracken may hamper the development of young trees. It invades new areas at a rapid pace; young plants develop up to 45 fronds (leaves) in the second year and about 140 in the third. Once established the underground rhizomes, which may be situated as deep as 60 cm below soil surface, keep producing new fronds for many years. Moreover, the plant produces allelopathic compounds. In South-East Asia it can be a weed in tea and other plantation crops. In Scotland, methyl (4-aminobenzenesulphonyl) carbamate, sprayed on the foliage is an effective means of control. Corticium anceps, Fusarium spp. and Septoria aquilina are parasitic fungi found on Pteridium aquilinum, and may form potential sources of biological control. Bracken has almost no serious insect enemies because it contains ecdysone which interferes with the moulting processes of insects.
Reproduction of Pteridium aquilinum is mainly by vegetative means, even though up to 300 million spores may be produced by a single leaf. When mature, spores are mechanically ejected 1–2 cm in the air during dry weather, dispersed by wind and often deposited with the first rain thereafter. The spores germinate without any period of dormancy. Young plants may be found after 6–7 weeks.
Statistics on production and trade of Pteridium aquilinum are scarce. In 1970 over 300 t bracken croziers were consumed in Tokyo alone, and in the whole of Japan annual consumption may have reached several thousand t. Only a few statistical data are available on its yield. It has been estimated that the annual rhizome production may amount to 17 t/ha. It has been calculated that 50 t of dried bracken are required to produce one t of potash.
Genetic resources and breeding
Being a cosmopolite Pteridium aquilinum is not in danger of genetic erosion. Germplasm collections and breeding programmes are not known to exist.
Prospects
The importance of bracken is mainly local and often only historical. The fact that all plant parts are suspected or confirmed poisonous limits their suitability for human consumption. In Africa the use of Pteridium aquilinum as food must therefore be discouraged or closely monitored, and health authorities should warn the local populations of its dangers. Most other uses are trivial, and many alternatives exist. It is not likely that the plant will increase in importance, certainly not in Africa, although its use as a natural pesticide seems to provide an as yet unknown opportunity for Africa. The medicinal and pesticidal qualities need further investigation.
Major references
• Haerdi, F., 1964. Die Eingeborenen-Heilpflanzen des Ulanga-Distriktes Tanganjikas (Ostafrika). In: Haerdi, F., Kerharo, J. & Adam, J.G. (Editors). Afrikanische Heilpflanzen / Plantes médicinales africaines. Acta Tropica Supplementum 8: 1–278.
• Kerharo, J. & Bouquet, A., 1950. Plantes médicinales et toxiques de la Côte d’Ivoire - Haute-Volta. Vigot Frères, Paris, France. 291 pp.
• Koagne, H., 1999. La dynamique des plantes et dérivés alimentaires dans la Chefferie Bafoussam. Abstract in: Mnzava, N.M., Dearing, J.A., Guarino, L. Chweya, J.A. & de Koeijer, H. (Editors). Bibliography of the genetic resources of traditional African vegetables. Neglected leafy green vegetable crops in Africa. Volume 2. IPGRI, Nairobi, Kenya. p. 56.
• Raponda-Walker, A. & Sillans, R., 1961. Les plantes utiles du Gabon. Paul Lechevalier, Paris, France. 614 pp.
• Titien Ngatinem Praptosuwiryo & Jansen, P.C.M., 2003. Pteridium aquilinum (L.) Kuhn. In: de Winter, W.P. & Amoroso, V.B. (Editors). Plant Resources of South East Asia No 15(2). Cryptogams: ferns and fern allies. Backhuys Publishers, Leiden, Netherlands. pp. 161–166.
Other references
• Alston, A.H.G., 1959. The ferns and fern-allies of West Tropical Africa. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. 89 pp.
• Cody, W.J. & Crompton, C.W., 1975. The biology of Canadian weeds. 15. Pteridium aquilinum (L.) Kuhn. Canadian Journal of Plant Science 55: 1059–1072.
• d’Oliveira Fejiâo, R., 1960. Elucidário fitologico. Plantas vulgares de Portugal continental, insular e ultramarino. Classificão, nomes vernáculos e aplicações. Volume 1, A–H. Instituto Botânico de Lisboa, Lisbon, Portugal. 472 pp.
• Everist, S.L., 1974. Poisonous plants of Australia. Angus & Robertson, London, United Kingdom. 966 pp.
• Kingsbury, J.M., 1964. Poisonous plants of the United States and Canada. Prentice-Hall, Englewood Cliffs, NJ., United States. 626 pp.
• Nwosu, M.O., 2002. Ethnobotanical studies on some Pteridophytes of Southern Nigeria. Economic Botany 56(3): 255–259.
• Schelpe, E.A.C.L.E., 1970. Dennstaedtiaceae. In: Exell, A.W. & Launert, E. (Editors). Flora Zambesiaca. Pteridophyta. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. pp. 81–92.
• Tardieu-Blot, M.L., 1964. Dennstaedtiaceae. Flore du Gabon. Volume 8. Muséum National d’Histoire Naturelle, Paris, France. pp. 67–79.
• Tryon, R.M. & Tryon, A.F., 1982. Ferns and allied plants. Springer Verlag, New York, United States. 857 pp.
Sources of illustration
• Titien Ngatinem Praptosuwiryo & Jansen, P.C.M., 2003. Pteridium aquilinum (L.) Kuhn. In: de Winter, W.P. & Amoroso, V.B. (Editors). Plant Resources of South East Asia No 15(2). Cryptogams: ferns and fern allies. Backhuys Publishers, Leiden, Netherlands. pp. 161–166.
Author(s)
W.J. van der Burg
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
Based on PROSEA 15(2): ‘Cryptogams: Ferns and fern allies’.

Editors
G.J.H. Grubben
Prins Hendriklaan 24, 1401 AT Bussum, Netherlands
O.A. Denton
National Horticultural Research Institute, P.M.B. 5432, Idi-Ishin, Ibadan, Nigeria
Associate Editors
C.-M. Messiaen
Bat. B 3, Résidence La Guirlande, 75, rue de Fontcarrade, 34070 Montpellier, France
R.R. Schippers
De Boeier 7, 3742 GD Baarn, Netherlands
General editors
R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
L.P.A. Oyen
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
Illustrator
PROSEA
PROSEA Network Office, Herbarium Bogoriense, P.O. Box 234, Bogor 16122, Indonesia

Correct citation of this article:
van der Burg, W.J., 2004. Pteridium aquilinum (L.) Kuhn In: Grubben, G.J.H. & Denton, O.A. (Editors). PROTA 2: Vegetables/Légumes. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, plant habit; 2, cross section rhizome; 3, fertile part leaf segment.
Source: PROSEA