External flavones in sweet basil, Ocimum basilicum, and related taxa

Sixteen accessions of Ocimum basilicum L. belonging to different cultivars and varieties, and one accession each of O. X citriodorum Vis. and O. minimum L., were examined for their external leaf flavonoids. The O. basilicum samples showed the presence of one or two major flavone aglycones, which were identified as salvigenin and nevadensin, and up to 10 minor ones: cirsileol, cirsilineol, eupatorin, apigenin, acacetin, genkwanin, apigenin 7,4'-dimethyl ether, cirsimaritin, ladanein and gardenin B. No trace was found of xanthomicrol, the only lipophilic flavone so far reported from O. basilicum. There were appreciable differences amongst the accessions in total flavonoid concentration and in their nevadensin / salvigenin ratios, which, on the whole, were not correlated with morphological characters. The surface flavonoid profile of O. x citriodorum was very similar to those of the O. basilicum plants studied, but that of O. minimum was significantly different. Only 4'-methyl ethers of apigenin derivatives were detected in the latter taxon, whereas apigenin and luteolin derivatives in which the 4'-hydroxyls are free were absent. Furthermore, the ratio of nevadensin / salvigenin was much higher in O. minimum than in O. basilicum or O. X citriodorum. These differences support the treatment of O. minimum as a separate species rather than as a variety of O. basilicum. Copyright (C) 1996 Elsevier Science Ltd