The Geography of Phytochemical Races

198 4 Intercontinental Disjunctions
Hara, and hondoensis Honda in Japan. An examination of the polyphenolic constituents
of these four taxa revealed clear-cut differences between North American
and Japanese populations (Iwashima and Ootani, 1995). The overall profi le of
the species was shown to consist of C-glycosylfl avones based upon apigenin and
luteolin, secondary O-glycosides of some of these, O-methylated fl avones, and
the C-glucosylxanthones mangiferin and isomangiferin (see Fig. 2.38, page 63).
The Japanese varieties hondoensis and nasuensis exhibited identical profi les,
whereas the profi le of var. setosa lacked some of the secondary O-glycosides and
an O- glycosyl derivative of the xanthones. The profi le of the North American
material was very different, in that it lacked apigenin mono-C-glycosyl derivatives,
the secondarily O-methylated derivatives, and the O-methylated fl avones.
An O-glycosylated xanthone derivative was also present which was not observed
in the Japanese plants. The authors suggested that the polyphenolic data could be
taken to support recognition of Iris hookeri rather than to continue recognition of this
taxon at the level of variety. No comments were made vis-à-vis evolutionary relationships
among the four taxa.
4.3.7 Humulus lupulus (Cannabaceae)
The resins derived from female fl owers of Humulus lupulus L., known commonly
as hops, provide the bitter and aromatic components so essential for the brewing of
beer. According to Mabberley (1997), the genus consists of two species, H. lupulus
of northern temperate regions and H. japonicus Sieb. & Zucc. of temperate eastern
Asia. Owing to intense selection for fl avor and yield characteristics, many cultivated
varieties of H. lupulus have been developed. Although there is opinion to
the contrary, J. F. Stevens et al. (2000), whose chemical study is discussed below,
prefer the infraspecifi c taxa formally described by Small (1978). Thus, wild hops
of Europe are considered to be H. lupulus var. lupulus, while North American hops
are segregated into three varieties primarily on the basis of geography: H. lupulus
var. lupuloides E. Small from central and eastern North America, H. lupulus var.
pubescens E. Small from midwestern United States, and H. lupulus var. neomexicanus
Nelson and Cockerell of western North America. These are often referred to
generally as “wild American hops.” According to Stevens et al. (2000), the wild
hops of “Japan and perhaps eastern mainland Asia” can be referred to as H. lupulus
var. cordifolius (Miquel) Maximowicz.
In addition to the bitter acids and essential oils, the fl owers of hops offer a rich array
of polyphenolic compounds, primarily chalcones and their accompanying fl avanones,
many of which are prenylated derivatives (Stevens et al., 1997, 1999a, b). The most
prominent fl avonoid in all plants studied was xanthohumol [342] (3′-prenyl-6′-Omethylchalconaringenin;
chalconaringenin is 2′,4′,6′,4-tetrahydroxychalcone) (see
Fig. 4.11 for structures 342–346). Several additional chalcones—variously adorned
with O-methyl and/or C-prenyl functions—were also encountered, along with their
respective fl avanones. Three new compounds were described in the Stevens et al.