On the natural occurrence of gossypetin 7- and 8-monomethyl ethers

The 7-methyl ether of gossypetin occurs, as a mixture of 4 glycosides, in the yellow inflorescence of Eriogonum nudum. In contrast to previous reports, however, it does not occur in Lotus corniculatus flowers, nor is it present in leaves of Medicago sativa. The 8-methyl ether, which is present in Lotus flowers, has been found for the first time in the Compositae, in flowers of Geraea canescens.     

The systematic implications of the complexity of leaf flavonoids in the bromeliaceae

In a leaf survey of 61 species of the Bromeliaceae, an unexpectedly wide spectrum of flavonoid constituents was encountered. The family is unique amongst the monocotyledons in the frequency and variety of flavonoids with extra hydroxylation or methoxylation at the 6-position. More common flavonols (in 43% of species) and flavones (in 13%) are distributed throughout the family whereas the rarer flavonoid classes are restricted to one or two of the three subfamilies. Thus 6-hydroxyflavones were found in both the Pitcairnioideae (in 50%) and the Tillandsioideae (in 14%) but patuletin (in 19%), gossypetin (in 1 species) and methylated 6-hydroxymyricetin derivatives (in 24%) were detected only in the Tillandsioideae. A new flavonol, 6,3′,5′-trimethoxy-3,5,7-4′-tetrahydroxyflavone, was identified as the 3-glucoside in Tillandsia usneoides and a new glycoside, patuletin 3-rhamnoside, in Vriesea regina. Myricetin glycosides were found only in the Bromelioideae and their presence here and the concomitant absence of 6-hydroxyflavonoids could indicate the primitive condition of this subfamily. The flavonoid results, in toto, confirm the view based on morphology, that the Bromeliaceae occupies an isolated position in relation to other monocot families.     

Two gossypetin methyl ethers as ultraviolet patterning guides in the flowers of Coronilla valentina

The 3′-monomethyl and 8,3′-dimethyl ethers of gossypetin have been identified in the flowers of Coronilla valentine where they occur as the 3-rutinosides. These two yellow flavonols occur specifically in the wings and thus provide both visible yellow colour and UV absorption to bees, which land on the wings and trigger the self-fertilization mechanism. These yellow pigments are absent from the flowers of the related C. emerus, where their role in UV patterning is taken over by colourless kaempferol and quercetin glycosides.     

Anthochlor pigments and floral UV patterns in the genus Bidens

The occurrence of floral UV absorption-reflection patterns in Bidens laevis is due to a spatial segregation of anthochlor pigments in the flower head. Interspecific, UV pattern polymorphism within this genus falls generally along taxonomic (sectional) lines.     

The rare flavone isoetin as a yellow flower pigment in Heywoodiella oligocephala and in other Cichorieae

Isoetin (5,7,2′,4′,5′-pentahydroxyflavone) has been identified as a yellow flower pigment in Heywoodiella oligocephala, Hieracium pilosella and Hispidella hispanica. It also occurs in leaves of these plants and of 15 other taxa of the Cichorieae. It is restricted to three of the eight subtribes, occurring most characteristically in the Leontodontinae (in 5 of 7 genera surveyed). Isoetin is frequently accompanied by apigenin, luteolin, and scutellarein derivatives in these plants.