Flavonoid Evolution in Robinsonia (Compositae) of the Juan Fernandez Islands

Abstract

Leaf flavonoids were isolated and identified from 54 populations representing all seven species of Robinsonia, a genus of dioecious rosette trees endemic to the Juan Fernandez Islands. Fourteen compounds were detected consisting of flavonols, flavones, flavanones and dihydroflavonols. The distribution of these compounds in Robinsonia largely corresponds to specific and sectional limits based on morphological data. The morphologically similar species, R. gayana and R. thurifera, have identical flavonol profiles (derivatives of quercetin). Likewise, the closely related R. evenia and R. masafuerae are unique in the genus by possessing flavones. The inclusion of Rhetinodendron (i.e., R. berteroi) in Robinsonia is supported by its strong flavonoid similarity with species in two other sections of the genus. The morphologically diverse section Eleutherolepis exhibits the greatest flavonoid variation of any section, and only here are found flavones, flavanones and dihydroflavonols. The direction of flavonoid evolution in Robinsonia is hypothesized to be from fewer to more classes of compounds. Biosynthetic considerations suggest that this gain in compounds is due both to a gain of an additional enzymatic step and to the sequestering of precursors. This interpretation of direction of flavonoid evolution is in agreement with several lines of evidence including the flavonoid chemistry of the hypothesized outgroup (i.e., species of Senecio on mainland Chile), the ages of the two islands, and morphological trends.

Flavonoids of the Sunflower Family (Asteraceae)

“…Robinsonia: Robinsonia is a genus of seven species (Pacheco et al, 1985;Sanders et al, 1987) restricted to the Juan Fernandez Islands. The species have O-glycosides of naringenin, eriodictyol, dihydroquercetin (taxifolin), apigenin, luteolin, kaempferol, and quercetin.…”

“…A detailed study of all seven species, including R. berteroi, which was previously considered to constitute the monotypic genus Rhetinodendron, was described by Pacheco et al (1985). The flavonoid profile of the genus consisted of glycosides of apigenin, luteolin, kaempferol, quercetin, isorhamnetin, naringenin, eriodictyol, and dihydroquercetin (taxifolin).…”

Flavonoid Evolution in Dendroseris (Compositae, Lactuceae) From the Juan Fernandez Islands, Chile

“…Dendroseris appears to be an example where reduction in flavonoid chemistry has occurred during evolution, and contrasts with the reverse situation found in Robinsonia (Pacheco et al, 1985) where evolution seemingly has been accompanied by elaboration of the flavonoid profile mainly by accumulation of intermediate metabolites in flavonoid biosynthesis. Dendroseris appears to be an example where reduction in flavonoid chemistry has occurred during evolution, and contrasts with the reverse situation found in Robinsonia (Pacheco et al, 1985) where evolution seemingly has been accompanied by elaboration of the flavonoid profile mainly by accumulation of intermediate metabolites in flavonoid biosynthesis.…”

“…Mabry (1974) suggested that within genera the more advanced species tend to have both fewer flavonoid compounds and structurally more sim-ple compounds. In other genera, a trend toward greater flavonoid complexity seems to be the case, while in still other genera there appears to be no trend in either direction (Pacheco et al, 1985). In other genera, a trend toward greater flavonoid complexity seems to be the case, while in still other genera there appears to be no trend in either direction (Pacheco et al, 1985).…”

“…Gardner (1976) found intraspecific variation in polyploid species of Lipochaeta (Compositae) in Hawaii, but diploid members ofthe genus were uniform. Four species from the endemic genus Robinsonia (Compositae) were examined for flavonoids in seven to 21 populations (Pacheco et al 1985). Studies of endemic species in several genera from the Juan Fernandez Islands have revealed various levels of intraspecific flavonoid variation.…”