The Geography of Phytochemical Races

8 2 Examples Within Continents
each from Ghana, Kenya, Madagascar, Nigeria, Zambia, and Zimbabwe. The list of
identifi ed compounds comprises myristic, palmitic, and oleic acids, phytol palmitate,
phytol oleate, and phytol linoleate, α-tocopherol and the long-chain alkanes eicosane
(C 20 ), henicosane (C 21 ), tricosane (C 23 ), nonacosane (C 29 ), hentriacontane (C 31 ),
tritriacontane (C 33 ), and pentatriacontane (C 35 ). In addition to the named molecules,
22 unidentifi ed compounds were used in a statistical analysis. Interpretation of
the contour diagrams representing the data set within this species is left to readers
familiar with this analytical approach. Suffi ce it say, as the authors concluded,
that there is a signifi cant level of chemical differentiation evident on the continent.
Dealing strictly with average values, the authors noted that northeastern African
populations yielded 15.8–22.8% oleic acid compared to 1.8% in Zambian material.
Hentriacontane (C 31 ) concentration varied from 52.3% in Zambian populations to
11.3% for plants collected in Madagascar. The level of α-tocopherol in plants from
Zimbabwe was 5.8%, but only 1.4% in plants collected in Kenya (where the species
appears to be rare). A further distinction was noted in the concentration of the
phytol esters, which varied from 6.3 to 9.7% in Ghanaian plants, but reached no
higher than 4.5% (phytol oleate in Kenyan material) in any other specimen. For the
purpose of germplasm conservation, four areas were defi ned: (1) northeast Africa
comprising Ethiopia and Kenya; (2) Madagascar; (3) Southern Africa comprising
Zambia and Zimbabwe; and (4) West Africa comprising Ghana and Nigeria. It did
not go without notice that dispersal of seed of different chemotypes of this species
through human movement has been (and may still be) a contributing factor.
2.1.5 Aloë (Asphodelaceae)
Aloë is a genus of respectable size, with some 365 species distributed widely in Africa,
Madagascar, the Arabian Peninsula, and the Canary Islands (Mabberley, 1997, p. 26).
The taxa of special interest here are the shrubby species native to East Africa. Cutler
et al. (1980) undertook a multidisciplinary study of the group with an interest in,
among other things, the nature of the cuticular patterns on the epidermis of mature
leaves. This feature offers a useful means of identifying most species, with closely
related taxa exhibiting similar patterns. Twelve species were examined representing
sites in Tanzania, Kenya, and Uganda. Six of these were diploids (2n = 14), exhibiting
a range of morphological features, including the cuticular pattern. The other six, all
tetraploids (2n = 27, 28, 29), were morphologically very similar, which were taken to
suggest that they may have originated from a single source, possibly a diploid of the
form of A. morijensis Carter and Brandham. The choice of shrubby diploid progenitors
was narrowed from six to two on the basis of morphological features, A. morijensis
and A. fi brosa Lavranos and Newton. It was also seen as relevant that these two taxa,
along with A. babatiensis Christian and Verdoorn, yielded identical chromatographic
profi les. Aloë fi brosa was eliminated as a candidate owing to its large size. On comparison
of A. morijensis and the tetraploid A. kedongensis, Reynolds revealed such a
level of similarity that formation of the latter from A. morijensis by straightforward