The Geography of Phytochemical Races

2.1 Africa (Including Madagascar) 11
Leaves of A. linearis (Burm. F.) Dahlgren, provide the caffeine-free herbal “rooibos
tea.” Although cultivated commercially, this species occurs naturally. As pointed out
in their paper on chemical variants (van Heerden et al., 2003), the species is highly
variable with respect to habit, fi re survival, vegetative structures, reproductive morphology,
electrophoretic characteristics, and fl avonoids (see their paper for leading
references). Despite the availability of a variety of features, no infraspecifi c classifi -
cation has been agreed upon. The chemical study by those workers revealed several
profi les based upon, among others, the C-glycosides orientin, isoörientin, and vitexin,
quercetin glycosides, and aspalathin [18] (See Fig. 2.3). Aspalathin belongs to one of
the smaller groups of unusual fl avonoids—the C-glycosyldihydrochalcones. Perhaps
the most noteworthy fi nding was the observation that the combination of aspalathin
and one of the unidentifi ed fl avonoids appears to characterize certain populations
from the more northerly part of the taxon’s range. However, some plants from southern
populations did exhibit trace amounts of the dihydrochalcone along with major
amounts of the other compounds.
2.1.7 Mangrove Waxes
Preliminary studies of leaf waxes from species of Rhizophora (Rhizophoraceae)
in West Africa (Dodd et al., 1995) revealed a signifi cant level of variation in both
aliphatic hydrocarbons and triterpene derivatives. In the following year the work
was expanded to a comparison of wax components of mangrove species from
Gabon in West Africa, and Guyana on the northeastern coast of South America
(Rafi i et al., 1996). Most striking was the comparison between Avicennia germinans
(L.) L. (Avicenniaceae) from the two coasts. Triterpenes in the Guyana material
amounted to less than 2%, whereas these compounds in the plants from Gabon comprised
10–23% of total extract. The hydrocarbon fraction also showed large differences
with the C 28 fraction ranging between 38.6% and 66.7% for Guyanan plants
and between 10.9% and 23.1% for those from Gabon. The ranges were reversed
for C 32 hydrocarbons, with the values for Guyanan specimens ranging from 1.1%
to 2.0% and the Gabonese specimens weighing in the range of 16.8–28.4%. It is
interesting to note that some taxonomists have recognized the plants from Gabon
as Avicennia africana Beauv. in spite of the absence of clear morphological differences
between them and specimens from South America.
2.1.8 Papaver aculeatum (Papaveraceae)
The genus Papaver consists of 80 species (Mabberley, 1997, p. 525), nearly all of
which are Northern Hemisphere in occurrence. One species occurs in the Cape Verde
Islands and another, the subject of this entry, is found in South Africa and is naturalized
in Australia. Papaver aculeatum Thunb. (P. gariepinun Burch. ex DC; P. horridum
DC) occurs widely in South Africa in areas characterized by summer rainfall and