The Geography of Phytochemical Races

220 5 Wide Disjunctions
and, unrelated, the presence of a potent thiaminase I, which is the causative agent
in neuropathies observed in stock animals that have eaten bracken (W. C. Evans,
1986; Fenwick, 1988). A large literature has accumulated on the subject of the carcinogenic
compounds of bracken, among which are several that treat the chemical
structure of the compounds (e.g., Niwa et al., 1983; Ojika et al., 1987; K. Saito
et al., 1990), their action on DNA (Ojika et al., 1989), and analytical applications
(Alonso-Amelot et al., 1992). The main carcinogen from bracken, ptaquiloside
[391], and its conversion product, pterosin-B [392], are illustrated in Fig. 5.2.
Our interest focuses on more recent work by Alonso-Amelot et al. (1995) that
deals with the comparative dynamics of ptaquiloside and pterosin-B in two varieties
of P. aquilinum, var. caudatum and var. arachnoideum, both collected in Venezuela.
Whereas both varieties exhibit both compounds, the quantities present were shown
to be markedly different. Thus, in newly emerged crosiers, which have the highest
concentrations of these compounds among growth stages, the amount of ptaquiloside
in var. caudatum varied in the range 1.98–3.9 mg/g biomass, whereas var.
arachnoideum exhibited concentrations in the range 0.032–0.66. The concentrations
of these compounds drops as the plant ages, but the relative differences persist.
According to N. Tanaka et al. (1993), neither ptaquiloside nor pterosin-B was
present in var. esculentum collected in New Zealand (cited as Pteridium esculentum
in that paper). There is a reference in that paper, however, to work published in the
New Zealand Veterinary Journal [Smith et al., Vol. 36: 56 (1988)] not only concerning
the identifi cation of ptaquiloside as the component in P. esculentum responsible
for cattle poisoning in New Zealand but also noting its regional variation.
Other, simpler compounds appear to vary among varieties of bracken as well.
Both trans-o-coumaric acid [393] and the related coumarin [394] have been
reported from var. caudatum (Bohm and Tryon, 1967; Alonso-Amelot et al., 1995),
but not from other varieties that have been tested: var. aquilinum from Europe and
England, var. latiusculum from Europe, North America, and Japan, var. pubescens
from western North America and Mexico, and var. esculentum from Australia and
New Zealand (Alonso-Amelot et al., 1995).
Fig. 5.2 Compounds
391–394, constituents of
Pteridium aquilinum