The Geography of Phytochemical Races

2.1 Africa (Including Madagascar) 7
upon a long-distance dispersal event followed by differentiation of a daughter species,
or whether the two extremes represent relics of a once broader distribution. Other features
of these taxa would have to be studied in order to resolve that question.
2.1.3 Pearsonia (Fabaceae)
Pearsonia (Fabaceae, Crotalarieae) is a genus of 12 species in tropical and Southern
Africa with one in Madagascar (Mabberley, 1997, p. 535). Leaves of 59 specimens
representing nine species were examined for alkaloids by Van Wyk and Verdoorn
(1991). In all, eight compounds were detected. High levels of both qualitative and
quantitative variation were observed in this study and attributed to four phenomena:
(1) interspecifi c and intersubspecifi c differences; (2) developmental differences;
(3) organ differences; and (4) interpopulational (geographic) differences. As an
indication of the degree of geographic differences in alkaloid concentration in
P. cajanifolia (Harv.), Polhill subsp. cajanifolia, and subsp. cryptantha (Bak.)
Polhill collected in northeastern South Africa in the vicinity of Pretoria. Their data
can be found in Table 2.1. The four characteristic compounds identifi ed in this study
are 13α-hydroxylupanine [6]; 8α, 13α-dihydroxylupanine [7], cajanifoline [8], and
pearsonine [9] (See Fig. 2.2 for structures 6–9).
2.1.4 Phytolacca dodecandra (Phytolaccaceae)
Interest in chemical variation in Phytolacca dodecandra L’Hert. stems from its
potentially important biologically active constituents, perhaps the most signifi cant
of which is the molluscicidal compound “lemmatoxin.” Attempts to measure variation
within this taxon, which occurs widely on the African continent, have involved
a study of morphological features (Adams et al., 1989) and the comparative chemical
work to be described here (Adams et al., 1990). This more recent study involved
analysis of nonpolar constituents from three populations from Ethiopia, and one
Table 2.1 Percentage of alkaloids in leaves of Pearsonia cajanifolia from sites in South Africa
(after Van Wyk and Verdoom, 1991)
Taxa and Sites Cmpd-[6] a Subsp. cajanifolia
Cmpd-[7] Cmpd-[8] Cmpd-[9]
Kensington (no data) 25 22 54b – 8 12 8 –
Northcliff (26°9′S, 27°58′E) 38 16 13 – 16 20 19 –
Magaliesberg (26°S, 27°33′E)
Subsp. cryptantha
35 53 22 65 47 27 t – t –
Blydepoort (no data) t t t – t t – 99 85 99
Pilgrims Rest (24°55′S, 30°44′E) 8 40 23 – 5 t – t – –
Lydenburg (25°10′S, 30°29′E) 14 t 6 – 13 – – 7 1 –
a Compound numbers refer to structures in Fig. 2.1.
b Values are percent (%) for three plants from each population; t = trace.