The Geography of Phytochemical Races

24 2 Examples Within Continents
Knob (southern Canterbury Administrative Region; see Fig. 2.11) and cycloartenol
methyl ether [58] was found in plants from Clarke River, whereas four other collections
failed to yield any TMEs. Similarly, populations of C. rigida (Raoul) Zotov
from eastern South Island do not synthesize TMEs, whereas those from western
South Island were shown to accumulate β-amyrin methyl ether [59]. An additional
difference between populations from these two sites lies in the capacity of the former
to produce short-chain wax components, as opposed to long-chain compounds
from the latter (Cowlishaw et al., 1983). Different chemodemes were also described
for C. cheesemanii (Hackel ex Cheesem.) Zotov; plants from North Island exhibited
lupeol methyl ether as the dominant compound along with lesser amounts of arundoin
and two unidentifi ed compounds, whereas populations from the South Island
had arundoin as the major compound with lesser amounts of lupeol methyl ether.
The study by Cowlishaw et al. (1983) involved an examination of the epicuticular
wax chemistry of four species of the genus, C. fl avescens Zotov, C. pallens Zotov,
C. rigida, and C. rubra Zotov, with regard to the chain lengths of acids, alcohols, aldehydes,
alkanes, and wax esters. These compounds consist of long-chain, unbranched
hydrocarbons with the appropriate functional group at one end. Wax esters involve a
long-chain alcohol and a long-chain acid in a normal ester linkage. The major acids,
aldehydes, and alcohols identifi ed ranged between C 24 and C 32 , the alkanes ranged
between C 29 and C 33 , and the esters ranged between C 36 and C 52 (recall that these larger
numbers represent sums of alcohol and acid carbons). Differences in the profi les of
wax components led to the recognition of distinct chemical regions for the studied
taxa. For example, C. rigida assorted into eastern and western South Island types
(mentioned above with respect to TMEs). Three wax chemical types were evident in
C. fl avescens, one encompassing populations from Canterbury and near Nelson, a second
consisting of populations from the western part of South Island, and a third consisting
of populations from the southern part of North Island. Chemodemes were also
evident within both C. pallens and C. rubra, both of which sorted into four types. The
overall outcome of these studies was the suggestion that the northwest Nelson district
could be the center of biosynthetic diversity with diversifi cation having occurred along
three routes, one to the western part of the South Island, one to eastern South Island,
and one to the southern part of North Island. As differentiation proceeded, enzymes
involved in the elongation steps of fatty acid biosynthesis and those that catalyzed
decarboxylation underwent changes in their specifi city in response to selection pressures
in the respective environments. It would be of considerable interest to see what
gene sequence studies within this system would yield.
2.3 Europe
2.3.1 Ramalina siliquosa (Ramalinaceae)
Although this example represents one of the most thoroughly studied examples of
local chemical differentiation, a little background involving a broader area is useful