The Geography of Phytochemical Races

294 7 Polar Disjunctions
Table 7.1 Flavonoid aglycones from leaf surfaces of Larrea tridentata and L. divaricata (from
Mabry et al., 1977)
Flavonoid Larrea taxon studieda TRID DIV-A DIV-P
Flavones
Apigenin + + −
Apigenin 7-methyl ether + + −
Luteolin 7-methyl ether + + −
Luteolin 3′-methyl ether
Flavonols
+ + −
Kaempferol + + +
Kaempferol 3-methyl ether + + +
Kaempferol 7-methyl ether + + +
Kaempferol 3,7-dimethyl ether + + −
Kaempferol 3,4′-dimethyl ether + − +
Quercetin 3′-methyl ether + + +
Quercetin 3,7-dimethyl ether + + −
Quercetin 3,3′-dimethyl ether + + +
Quercetin 7,3′-dimethyl ether + + −
Quer. 3,7,3′-trimethyl ether + + −
Quer. 7,3′,4′-trimethyl ether + + −
Quer. 3,7,3′,4′-tetramethyl ether + + −
Herbacetin 3,7-dimethyl ether + − +
Gossypetin 3,7-dimethyl ether + − +
Goss. 3,7,3′-trimethyl ether
Dihydrofl avonol
+ − −
Dihydromyr. 3,5′-dimethyl ether + + +
a TRID = L. tridentata; DIV-A = L. divaricata from Argentina; DIV-P =
L. divaricata from Peru.
specimens of L. divaricata. Mabry et al. (1977, and others cited therein) suggest that
these results support the view that the isolation of the Peruvian population occurred
much earlier than the separation of the North American species. One can surmise
that the ancestral plants possessed the capacity for 8-oxygenation which gave rise
to the formation of the two 8-hydroxy fl avonols (herbacetin and gossypetin), which
is the major structural difference by which the L. tridentata-L. divaricata pair can
be distinguished from the other species. If, as suggested by Mabry et al. (1977),
the Peruvian populations arose through migration independent of the events that
gave rise to the North American taxon, the following scenario could account for the
observed profi le differences: (1) appearance of 8-hydroxylation in L. divaricata, or
a L. divaricata prototype; (2) dispersal to Peru, 8-hydroxylation maintained, some
depletion of capacity for O-methylation, and loss of capacity to make fl avones;
(3) independent dispersal to North America, and 8-hydroxylation maintained;
(4) loss of 8-hydroxylation by Argentinean plants; (5) polyploidization in North
American plants without changes to fl avonoid profi le.
Flavonoids glycosides of the genus were also studied in detail and again
L. tridentata, with 17 of the 18 identifi ed compounds, exhibited the most complex
array. The close relationship between L. tridentata and L. divaricata was again