The Geography of Phytochemical Races

5.2 Nonvascular Plants 221
Although this next example does not fi t into the category of wide disjunctions,
it does fall within the realm of bracken biology, if one takes a broad view. A recent
study by Alonso-Amelot et al. (2004) revealed interesting responses of bracken
species to different environments. Those workers measured concentration differences
in two taxa, P. caudatum (L.) Maxon and P. arachnoideum (Kaulf), that
occur naturally over different elevational gradients, sea level to 3200 m for the
former, 1800–3200 m for the latter. High-molecular-weight phenols (HMP) and
low-molecular weight phenols (LMP) were measured in samples collected along
gradients for each taxon. Synthesis and accumulation of LMP was found to be
largely independent of elevation, whereas HMP varied with elevation in both taxa.
The authors suggested two explanations for the observed results, either higher
production from UV-B from HMP than LMP, or differences in activity of lightactivated
steps in biosynthetic steps leading to the two types of phenols.
5.2 Nonvascular Plants
5.2.1 Pseudevernia furfuracea (Parmeliaceae)
The next several entries feature examples from the lichen literature. Study of chemical
constituents of lichens has proved an invaluable source of information on relationships
within this widespread group of organisms. The fi rst example, Pseudevernia
furfuracea (= Parmelia furfuracea) involves a disjunction across the Atlantic Ocean,
but other examples in this set enjoy much wider—and often unusual—disjunctions.
This example is included here in order to keep the lichen material in one place.
Hale (1956, 1968) reported different lichen acid profi les from specimens of
P. furfuracea that were morphologically identical. European material afforded two
compounds, olivetic acid [395] and its phenolic coupling derivative physodic acid
[396] (see Fig. 5.3 for structures 395–405). Plant material in North America, however,
yielded only lecanoric acid [397], which is not closely related biosynthetically
to the compounds from the European plants, although, of course, they all belong to
the same general class of metabolites. Based upon the chemical differences between
materials from the two sources, a suggestion was made that the two entities should
be recognized as different species (Hawksworth and Chapman, 1971; Hawksworth,
1976). Other information suggested that the taxonomic problem might not be so
easily resolved. C. F. Culberson (1965) had reported that 0.5% of individuals in a
Spanish population had acids of both types.
5.2.2 Rhizoplaca melanophthalma (Lecanoraceae)
Rhizoplaca melanophthalma (Ram.) Leuck. & Poelt seems to be a somewhat more
straightforward case of the existence of chemical races. Earlier work had shown