The Geography of Phytochemical Races

260 6 Oceanic Islands
compounds with the styryl double bond reduced (making it the 2-phenylethyl function)
as seen in 7,8-dihydrokawain [548], compounds with a second double bond in
the lactone moiety, as seen in 5,6-dehydrokawain [549], are also known, and compounds
in which the aromatic ring is substituted, such as in yangonin [550], which
bears a methoxy function at the p-position. Several kavalactones are characterized
by the methylenedioxy function, as seen in methysticin [551] and in dihydromethysticin
[552]. Other members of the family combine these functional groups in
various ways. The six compounds illustrated, however, are the most commonly
encountered ones, often constituting 95% of the total lactone content of a particular
cultivar.
Kava has been the subject of detailed study by several workers, whose interests
have included usage of the preparations in Hawaii (Titcomb, 1948); pyrone analysis
(Young et al., 1966); physiology of action of the constituents (Hänsel, 1968); monographic
study (Chew, 1972); cultivation (Lebot and Cabalion, 1986); origin of the
Oceanian plant (Lebot and Lévesque, 1989); genetic control of kavalactone chemotypes
(Lebot and Lévesque, 1996a); and relationships with the related P. wichmannii
C. DC. (Lebot and Lévesque, 1996b). Comprehensive citation lists can be found in
the papers by Lebot and Cabalion (1986) and Lebot and Lévesque (1989).
Lebot and Lévesque’s 1989 work was based upon an exhaustive collection
of plant material. Piper wichmannii was obtained from Papua New Guinea, the
Solomon Islands, and Vanuatu, which comprises its natural range. Piper methysticum
was collected from cultivated plots on three islands representing Micronesia,
eight representing Melanesia, and 24 from Polynesia. In all, more than 240 individual
plant acquisitions were subjected to chemical and morphological analysis.
The fi rst problem addressed by Lebot and Lévesque (1989), in their comprehensive
ethnobotanical study, dealt with the taxonomic status of P. methysticum and
P. wichmannii C. DC. Problems that had to be dealt with included the nearly total
absence of female plants, even in cultivation, and the complete lack of sexual reproduction
of P. methysticum in cultivation, and consequently, the absence of seeds.
Piper wichmannii, on the other hand, sets normal seed that germinate and develop
normally. Furthermore, morphological differences are slight, certainly not suffi cient
for specifi c recognition. Both species appear to be decaploids with 2n = 10x = 130
chromosomes (Jose and Sharma, 1985; Okada, 1986). The high ploidy level in
P. methysticum cannot be taken as explanation for the sterility of the cultivars, since
P. wichmannii, also decaploid, reproduces normally. Electrophoretic studies of both
species (Lebot et al., 1991; Lebot and Lévesque, 1996b) revealed a reduced level of
genetic variability within P. methysticum; only four of eight enzyme systems examined
were polymorphic, whereas all systems tested in P. wichmannii were polymorphic.
These studies provided important information relevant to the area of origin of
P. methysticum. Multivariate analysis of presence/absence of “electromorphs” indicated
that P. wichmannii from the Western Province of Papua New Guinea are very
different from those of P. methysticum, suggesting that the cultivated form did not
originate from that area. The closest “match” came from cultivated plants collected
in Vanuatu and southern Papua New Guinea, an observation that the authors took to
indicate that cultivated kava might have had its origin in that general area.