The Geography of Phytochemical Races

5.2 Nonvascular Plants 231
concentrations from Scottish sites varied from 15 to 29% compared with levels that
did not exceed 1% in samples from the Azores.
A more recent paper by Rycroft and Cole (2001) described a study of
Plagiochila rutilans Lindenb. From Bolivia, Brazil, and Costa Rica (all freshly
collected) and Cuba and Ecuador (dried specimens). Material from Cuba had
been described by Huneck et al. (1984) to contain, among other compounds,
1-(3,4-dihydroxy-5-methoxyphenyl)-3-methylbut-2-ene. In the recent paper,
Rycroft and Cole present evidence that the correct structure of the compound
is 1-(2,5-dihydroxy-3-methoxyphenyl)-3-methylbut-2-ene, which can also be
called 2-methoxy-6-prenylhydroquinone. The corresponding quinone was also
observed as a minor constituent.
Recent work identifying Plagiochila retrorsa Gottsche from collections made in
the Azores and Madeira establishes a signifi cant range extension for a taxon, known
under several other names, which occurs in the southern Appalachian Mountains and
in Costa Rica. Rycroft et al. (2001) described morphological and phytochemical characteristics
of representative specimens of this liverwort. Phytochemically, P. retrorsa
belongs to the 9,10-dihydrophenanthrene chemotype species (major structural type
is that of compounds 449 and 450).
5.2.9 Marchantia (Marchantiaceae)
Bibenzyl derivatives were met above with Plagiochila killarniensis. Some
liverworts, as we will now see, take this type of structure a step or so further
to yield dimeric compounds known as cyclic bis(bibenzyls). These compounds
have played a role in understanding relationships within the genus Marchantia
from which work has emerged interesting geographic patterns. Asakawa et al.
(1987) reported geographical differences in profi les of M. polymorpha plants
collected in Japan compared to others collected in France and India. The major
compound in Japanese plants, called marchantin-A, is shown as structure [454],
whereas the major compound from plants collected in the other two areas, known
as marchantin-E, is shown as structure [455] (see Fig. 5.7). The structural difference
between these two compounds is small, but two biosynthetic steps are
required, one to establish oxygen at the position marked “R” in the fi gure, and
a second to place the methyl group on that oxygen. This, of course, implies two
enzyme steps.
Marchantia brachiata (Sw.) Schiffn. is a liverwort that also enjoys a wide distribution.
It is included here to offset the idea that liverworts of wide occurrence need to
exhibit different chemistries in order to attract attention. Nagashima et al. (1999) identifi
ed four compounds from plants collected in Ecuador: 3,4-dimethoxystyrylbenzene
[456], 2,4,5-trimethoxystyrylbenzene [457], β-caryophyllene [458], and bicyclogermacrene
[459]. In the words of those workers, there was “… ostensibly no metabolic
differences between Marchantia brachiata collected in the Netherlands Antilles,
Saba, and in Ecuador.”