Comparative dynamics of ptaquiloside and pterosin B in the two varieties (caudatum and arachnoideum) of neotropical Bracken Fern (Pteridium aquilinum L. Kuhn)

Significant chemical differences have been observed among the two neotropical varieties of bracken, caudatum and arachnoideum. Trans-o-hydroxycinnamic acid and coumarin have been found only in the caudatum variety. The concentration changes of ptaquiloside and pterosin B with blade growth were markedly different in caudatum and arachnoideum. In the newly emerged croziers where the concentration of these compounds was highest the former exhibited from 1.98 to 3.9 mg of ptaquiloside per gram of biomass (mg/gbm) while arachnoideum possessed only between 0.032 and 0.66 mg/gbm. These concentrations decreased consistently with the unfurling of the blade. Pterosin B was found in approximately one-tenth of the ptaquiloside concentration in most stages, suggesting that these compounds are chemically related in vivo. Caudatum, in retaining a much higher concentration of these toxins than arachnoideum in the full grown frond poses a higher risk of exposure to farm grazing animals that the latter, where ptaquiloside and pterosin B are almost absent.