Not to be confused with : Bur-marigolds such as Nodding Bur-Marigold (Bidens cernua) or London Bur-Marigold (Bidens connata) or with Corn Marigold (Glebionis segetum) which have similar names and also belong in the same Asteraceae family, but which are all yellow.
Uniquely identifiable characteristics
Distinguishing Feature :
No relation to : Marsh Marigold (Caltha palustris) [a plant with similar name belonging to the Buttercup Family (Ranunculaceae)].
Grown in gardens it is not a plant native to the UK. Occurs as both the single flowered and double-flowered versions and can escape, although whether or not they were planted or thrown out into the wild is debateable, but once there, they do self-seed themselves and spread laterally. An annual that sometimes behaves as a perennial, sometimes over-wintering particularly in the warmer South or West of England, although it cannot tolerate conditions that are too hot.
The petals are edible and are used as a substitute for saffron in cooking rice, making soups or a tea infusion and taste almost of hops. Or used as an edible decoration with rose petals or borage flowers on cakes, salads, desserts or added in the making of cheese or butter. The flower has a faint aromatic smell The leaves too are edible, but not very palatable.
The petals will also yield a dye for fabrics such as wool, cotton, linen, silk and hemp which can be made yellow, orange or brown depending upon the mordant used. The Vikings used it to dye their hair fair. The petals (and pollen) contain the orange/yellow carotenoids
Auroxanthin and the clear Lutein (20%).
Both leaves and stems also contain other carotenoids: Zeaxanthin at 5% and Lutein at 80%.
Flavoxanthin is a golden-yellow pigment that is used as food colourant E161a in Australia and New Zealand but is not approved for use in the European Union or USA. (It does not contain the chemical moiety Xanthine which is an alkaloid containing four atoms of nitrogen which is based upon
Your Author can only guess that Auroxanthin, with a larger moiety at each end, will vibrate at a slightly lower frequency and thus absorb light wavelengths with longer wavelengths, putting the reflected light into the orange part of the spectrum.
Note that each have at least one (Auroxanthin has two) epoxy linkages across part of the molecule. This would tend to make them more chemically reactive, therefore probably more deleterious within the human body. Lutein has no epoxy linkages and double-bonds in some slightly differing positions.
Lutein is another Xanthophyll, but one which is colourless (white in powder form).
A FATTY ACID
The oil from the seeds (which are pale-brown, curved and have spines on the back) contains
Calendic Acid, a long-chain fatty acid, and is sometimes but rarely extracted commercially as an oil-seed crop for use in protecting the skin.