The Geography of Phytochemical Races

290 7 Polar Disjunctions
Fig. 7.3 Compounds 590–601, fl avonoids of Chrysosplenium, and simple phenolic derivatives
from Encelia
7.4 Encelia canescens (Asteraceae)
Encelia consists of some 15–19 species, depending upon one’s point of view, with
all but two occurring in arid and semiarid portions of southwestern North America.
One of those exceptions is Encelia canescens Lam., which occurs in coastal Peru
and Chile and in northern inland Argentina. In an examination of 19 taxa for their
chromones and benzofurans, Proksch and Clark (1987) observed four groups of
species. The South American taxon exhibited the same array of compounds as did
nine of the North American taxa, including a dimeric compound unique to this
group and to the genus. The compounds identifi ed are the chromones [593–595]