The Geography of Phytochemical Races

6.2 The Hawaiian Islands 249
distinguish it from species of Lycopersicon native to mainland South America.
There has been suffi cient morphological differentiation, however, to justify recognition
of L. cheesmanii f. minus (Hook. f.) C. H. Müll. An electrophoretic study
of four enzyme systems revealed low genetic variation within populations, but
quite high levels between populations. The electrophoretic profi le of L. cheesmanii
showed greatest similarity to L. pimpinellifolium (Jusl.) Mill., a species native to
northwestern Peru (Rick and Fobes, 1975). Further support for the suggestion that
L. cheesmanii and L. pimpinellifolium are closely related came from chloroplast
DNA restriction fragment analysis (Palmer and Zamir, 1982), which showed that
these two taxa comprise a clade that was a sister group to L. esculentum L. Because
we are primarily interested in small molecules in this review, it is interesting that the
three species involved in this study are characterized by red-orange fruit suggesting
similar carotene biosynthetic pathways.
6.1.3 Scalesia (Asteraceae)
Scalesia Arn. is a genus of 15 species endemic to the Galapágos Islands (Schilling et al.,
1994). The presence of trifi d pales, gummy resin, and a tetraploid chromosome number
of 2n = 68 for all members of the genus have led to the suggestion that Scalesia is monophyletic
(Eliasson, 1974). Schilling et al. (1994) undertook a restriction site analysis of
chloroplast DNA isolated from S. pedunculata Hook. f. and from species of Pappobolus
and Viguiera, genera thought to be closely related to Scalesia. Three species each of
Encelia and Flourensia were used as outgroups. In addition to confi rming the position
of Scalesia within Helianthinae, the DNA also identifi ed Pappobolus as its sister group,
although there were some cautionary comments included in their discussion. Nonetheless,
the authors used the sequence differences, 0.19%, to estimate time of divergence
of Scalesia from Pappobolus. Taking the estimated rates of evolutionary change for
cpDNA to be in the range of 0.03–0.19%, the time of divergence between Pappobolus
and Scalesia lies between 1.9 and 6.3 million years. This period of time is well within
the estimated age of the Galapagos Islands. Another interesting point was made by
Schilling et al. (1994), namely, that the time accords well with the estimated time of
appearance of the land bridge between North America and South America at about
3 mya. Establishment of a bridge between these two landmasses would have provided a
means of overland migration of the ancestor common to Pappobolus and Scalesia from
Mexico, which has been suggested as the region of origin of Helianthinae.
6.2 The Hawaiian Islands
The Hawaiian Islands have, arguably, attracted more scientifi c attention than any
other archipelago on the planet. Their unique fl ora has offered, and continues to
offer, a wide spectrum of challenging problems associated with one of the highest