The Geography of Phytochemical Races

2.1 Africa (Including Madagascar) 9
autotetraploidization seemed a reasonable suggestion (Cutler et al., 1980). This event
was thought to have occurred in the Morijo region of southwestern Kenya, followed
by colonization northward up the Rift Valley, with branches to the east in the vicinity
of Mt. Kenya and to the west into Uganda.
Chromatographic analyses in this genus have taken advantage of the presence
of a class of leaf exudate compounds known as aloins. Barbaloin [10] (See Fig. 2.3
for structures 10–17), nataloin [11], and homonataloin [12] are typical members of
this group of anthrone derivatives. Accompanying the anthrones in these plants are
compounds such as aloesin [13] and aloenin [14]. Comparative chromatographic
studies of the diploid and tetraploid shrubby aloes described by Reynolds (1986,
1990) support the origin of the tetraploids as suggested by Cutler et al. (1980).
The second study of Aloë involved the distribution of the naphthalene derivative
“plicataloside” [15], fi rst identifi ed by Wessels et al. (1996) as a component
Fig. 2.3 Compounds 10–17 from Aloë; Compound 18 from Aspalathus linearis; Compound 18.1
from Papaver aculeatum