Contemporary systematic treatments of the Central and South American bracken ferns in the genus Pteridium Gled. ex Scop. recognize morphotype caudatum as either a full species or a variety of P. aquilinum (L.) Kuhn. Geographically representative sporophytes of morphotype caudatum, including the type in the Linnaean Herbarium, are shown using spore size, guard‐cell length and morphology of the cells of the false indusium to be tetraploid (based on 4n = 208). DNA fingerprinting of field‐collected Venezuelan samples supports the generalization that morphotype caudatum is a fertile allotetraploid containing genomic elements otherwise distinctive of the southern hemisphere diploid P. arachnoideum (Kaulf.) Maxon, together with elements characteristic of northern hemisphere diploids including the North American P. aquilinum var. pubescens Underw. and P. aquilinum var. pseudocaudatum (Clute) A. Heller. Evidence of genetic isolation from taxa with overlapping distributions, as well as morphological, biochemical and ecological data, validate recognition of P. caudatum (L.) Maxon at species level. Heterogeneity observed within P. caudatum is consistent with multiple origins through independent hybridization events. Pteridium caudatum is strikingly analogous to the tropical Asian/Australasian allotetraploid P. semihastatum (N. Wallich ex J. G. Agardh) S. B. Andrews [=P. yarrabense (Domin) N. A. Wakef.]. © 2002 The Linnean Society of London. Botanical Journal of the Linnean Society, 2002, 140, 237−248.

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The complex taxon embraced in the Pteridium genus, popularly known as bracken fern and notorious weeds in many parts of the world, is one of the few vascular plants known to induce cancer naturally in animals. It has been known for long to be acutely toxic to livestock and sublethal chronic oral feeding of bracken fronds leads to cancerous lesions in the urinary bladder, or bovine enzootic haematuria (BEH) and ileum of cattle. Bracken poisoning has been attributed chiefly to ptaquiloside, a norsesqui-terpene which is also a potent carcinogen inducing various malignancies in laboratory animals. It is capable of alkylating uncoiled DNAbases at key proto-oncogenes of selected organs. Some human populations also eat young bracken shoots and epidemiological studies in Japan and Brazil have shown a close association between bracken consumption and cancers of the upper alimentary tract. In addition, other studies reveal that the mere presence of bracken swards represents a greater risk to die of gastric adenocarcinoma for people who live more than 20 years in such areas or are exposed in childhood. This work reviews the bracken-cancer connections established by in vitro and in vivo experiments and epidemiological studies in various parts of the world, and provides insights into the possible bridges for bracken carcinogens to reach the human diet. Also, specific points where more research is needed are highlighted.

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-The content of ptaquiloside (ptaq), a major Pteridium aquilinum carcinogen found in milk from cows fed bracken in Venezuela, has been estimated quantitatively in ils passage through bovines into milk. Six cows were given 6 kg/animal/d of fresh bracken fronds whose ptaq content was determined. Ptaq first appeared in milk 38 h after initially feeding this plant to the cows and continued to be excreted at a relatively constant level, after an induction period, for 62-70 h after the bracken diet had ceased. The average value of total ptaq excreted ([ptaq]e) from milk amounted to 8.60 ± 1.16 % of the total ptaq ingested ([ptaq]) during the entire feeding period.[ptaq]e was linearly dose dependent in the 2 400 to 10 000 mg/animal/d range of ptaq given to the test animais and the ratio [ptaqle/jptaq], remained relatively constant at various ptaq dosages. In a two-pulse feeding sequence with a 72-h interlude when no bracken was given, a bimodal ptaq excretion curve was obtained. The implications to human health are discussed. © InralElsevier, Paris ptaquiloside / bracken fern / cow's milk Résumé -Excrétion du ptaquiloside dans le lait de vaches alimentées avec de la fougère Bracken, Évaluation quantitative. La quantité de ptaquiloside (ptaq), le principal carcinogène de Pteridium aquilinum, retrouvé dans le lait de vaches alimentées avec la fougère bracken au Venezuela, a été estimée quantitativement. On a donné à six vaches 6 kglj de frondes fraîches de fougère, dont le contenu en ptaq a été deterrniné. Le ptaq est apparu d'abord dans le lait 38 heures après la première prise et a continué à être excrété à une concentration plus ou moins constante après une période d'induction, jusqu'à 62-70 heures après que l'alimentation en fougère a cessé. Ensuite, le ptaq a graduellement diminué jusqu'à ce qu'il ait disparu du lait. La valeur moyenne de ptaq excrétée dans le * Correspondence and reprints.