The Geography of Phytochemical Races

3.1 North America 135
Two species concern us in this discussion, M. ferruginea Smith from western North
America and M. pilosa (Michx.) Juss. from eastern North America. The western taxon
has been further subdivided into var. ferruginea, which occurs along the coast from
Alaska south to northern California, and var. glabella (Gray) Peck, which is native
to the Rocky Mountains. However, there has been some difference of opinion as to
the level at which the variation in the species should be recognized. Hickman and
Johnson (1969) argued for the elimination of infraspecifi c recognition; Peck (1961)
treated them as varieties, whereas Calder and Taylor (1956, 1968) recognized them
as subspecies. Menziesia pilosa consists of only the single taxon and is native to the
Appalachian Mountains. Two more recent studies of the North American members of
the genus have been described, one that focused on the fl avonoids (Bohm et al., 1984),
and one that concerned itself with allozyme variation (Wells and Bohm, 1994).
Extensive collections of both species (all taxa) provided an opportunity to examine
the fl avonoid profi les in detail. In addition to the almost ubiquitous presence of
the “usual suspects,” glycosides of kaempferol, quercetin, and myricetin (general
structures above), the dihydrofl avonol dihydromyricetin [270], the fl avanone [271],
and the unusual fl avonol gossypetin [272] were identifi ed (see Fig. 3.4). Dihydromyricetin
was observed only in the eastern species, whereas gossypetin was seen
only in the western species. Insofar as dihydrofl avonols are part of the normal fl avonol
biosynthetic pathway, the presence of dihydromyricetin may only refl ect a
concentration effect (sequestration is the term usually used for this). Gossypetin,
however, having an oxygen function at a position (C-8) represents a unique biochemical
step.
Structural data of fl avonoids from several hundred individual plants were analyzed
by a variety of statistical and multivariate techniques. Whereas signifi cant
differences were noted between the eastern and western species, the level of variation
within and between populations in each species was such that no pigment races
could be defi ned. Plants from Alaskan populations of M. ferruginea, for example,
were as likely to emerge next to populations from California or Oregon in these
treatments, as they were to emerge near populations from the northern or southern
Rocky Mountains. The number of combinations of fl avonoid pigments observed in
each species nearly equaled the number of populations examined, a level of variation
that approximates that described by Levy and his collaborators for species of
Phlox, as mentioned above. A good deal more insight into the Menziesia story came
from electrophoretic studies.
Fig. 3.4 Compounds 270–272, fl avonoids from Menziesia