The Geography of Phytochemical Races

108 2 Examples Within Continents
with latitude in the southern part of the transect (r = 0.740, P < 0.01), whereas in the
northern part of the range there was no signifi cant correlation (r = 0.264).
Subsequent papers on Satureja douglasii terpenes (Lincoln and Langenheim,
1979, 1981) addressed the question of what effect environmental factors might have
on the expression of the chemical forms, and what the genetic basis of the different
chemical forms is, respectively. In the fi rst of these studies, the effects of light
intensity and degree of herbivory were assessed. It was shown that high-yielding
genotypes tend to occur under low light-high herbivore pressure, whereas lowyielding
genotypes occurred under high light-low herbivore pressure. Attempts to
establish the genetic basis for monoterpenoid composition were not conclusive, but
did suggest that tight genetic control does function in this system. Despite the limited
conclusions concerning the genetics of the system, this study of Satureja douglasii
represents one of the better-documented examinations of secondary metabolite
profi le variation available in the literature.
2.7.16 Pentagramma (Pityrogramma) triangularis (Adiantaceae)
Pentagramma triangularis (Kaulf.) Yatskievych, Windham, and Wollenweber, the
most recent taxonomic reincarnation of Gymnogramma triangularis Kaulf. (see discussion
below), is a member of the fern family, Adiantaceae. This fern is characterized
by copious amounts of solid exudate (often called a farina) on the undersides
of its leaves, which has given rise to the common names of silverback or goldback
fern, depending upon the color of the material present. The taxon occurs in rock crevices
and open rocky slopes from southern British Columbia (Vancouver Island, Gulf
Islands, and only very rarely on the mainland; author’s comments) to northern Baja
California, east into Arizona, southern Nevada, and in extreme southwestern Utah
(Hitchcock et al., 1969). Since the range of occurrence of this fern, at least along the
coast (refer to Fig. 2.67 for general area map), is very similar to that of Satureja douglasii,
it seems appropriate to discuss differentiation of its chemotypes at this point.
Before getting to the chemical and related studies of this system, a note on recent
taxonomic work is in order. This species was fi rst described as a member of Gymnogramma
in 1824, but was placed in Pityrogramma in 1913 (see Yatskievych et al.,
1990 for generic taxonomic details; D. M. Smith et al., 1971 for varietal/subspecifi c
details). Questions have been raised, however, as to the inclusion of P. triangularis
(Kaulf.) Maxon in the genus. It was pointed out by Tryon (1962) that this taxon does
not fi t comfortably with the “central group” of species in the genus, and suggested
that it might well stand on its own, but did not make any formal change to its status.
This position was echoed by Tryon and Tryon (1982), but again no formal changes
were made owing to lack of suffi cient information. The problem was addressed by
Yatskievych et al. (1990) who assembled information on rhizome scale features, stipe
structure, laminar shape, shape of pinnae, venation, spore structure, and base chromosome
number in support of the recognition of the taxon as Pentagramma triangularis
consisting of four subspecies: triangularis, viscosa, semipallida, and maxonii.