The Geography of Phytochemical Races

88 2 Examples Within Continents
The overall mean number of steps per population is 19.53 and the overall mean
MBSD is 14.12. Comparative mean values for the separate ranges of P. carolina are:
continuous range = 13.14 ± 4.95 (N = 2016), disjunct range = 15.42 ± 6.40 (N = 36),
and continuous versus disjunct populations = 17.47 ± 3.90 (N = 576). These differences
are signifi cant (P < 0.001). These values indicate that the separate ranges of
the species are distinctive, but only weakly divergent with regard to their fl avone
profi les. Although there are no discrete patterns of fl avonoid profi les, some areas in
the continuous range show higher profi le uniformity than others. Of particular note
are populations in western Georgia, where similarities in the range 85–100% were
observed. However, even in that area, adjacent populations may not be the most
closely related, and those that are closely related may be separated by some distance
(ca. 50 miles). Although differences in pigment profi les were found within this species,
no clear-cut pigment races exist.
This fi nding is in general accord with aspects of the biology of the species. Levy
and Fujii (1978) pointed out that restricted gene fl ow is characteristic of Phlox,
which lacks the capacity for long-distance dispersal. They pointed out that the irregular
occurrence of most of the compounds suggested that the gradients observed
represent the results of “range dissection and contraction rather than stepping-stone
dispersal from central or local centers of fl avone diversity.” The result would be a
collection of local “islands” of fl avone diversity, which, through local expansion,
might come into contact with nearby populations to produce the complex array of
variants seen.
This study of Phlox carolina represents one of the best examples in the fl avonoid
chemosystematic literature where workers combined thorough sampling, detailed
statistical analysis, and an intimate knowledge of the biology of the system under
scrutiny to produce a convincing picture of natural variation. As mentioned at the
beginning of this discussion, a more casual approach would have undoubtedly overlooked
the subtle differences that characterize this system.
2.7.5 Lasthenia (Asteraceae)
Lasthenia Cass. is mostly a Californian genus of about 17 species; the single species
that occurs in Chile will be dealt with in the section on north–south disjuncts
below. An examination of fl avonoid pigments of all members of the genus (Bohm
et al., 1974) had shown that sections, defi ned on the basis of morphology, cytology,
and breeding behavior (Ornduff, 1966), could also be distinguished on the basis of
the presence or absence of a variety of fl avonoids (Bohm et al., 1974). For example,
sections Baeria (both species), Burrielia (all three species), and Hologymne (two
of three species) were characterized by an array of chalcone and aurone derivatives
(collectively referred to as anthochlors), in addition to a number of common
fl avones and fl avonols, whereas members of the other three sections exhibited only
fl avonols. The initial studies suggested that each section was characterized by a
unique combination of pigments. Some indication of variation did emerge from