No relation to : Flaxes such as Cultivated Flax (Linum usitatissimum) [plants with similar names belonging to differing families].
Hybridizes with : Pale Toadflax (Linaria repens) to produce
Linaria × sepium which has pale yellow flowers with violet veins.
Common Toadflax (sometimes called Yellow Toadflax) is by far and away the most common toadflax in the UK. It contains the
Vasicine (aka Peganine),
DeOxyVascinone (Vasicine without the -OH group), and 1,2,3,9-tetraHydroPyrrolo(2,1)Quinazolin-1-Carboxylic Acid. It also contains Syringin and the lignan glycoside
Liriodendrin, for which your author can find two differing structural formulae...
Native to Eurasia, Common Toadflax may have been introduced to the UK as a garden plant. It is a short-lived perennial and produces extensive, creeping rhizomatous roots, growing in dense patches. Because of this propensity to spread, in some parts of the world it is classed as an invasive species. Habitat includes grassy banks, road verges and waste places.
The seeds form in a brown and two-celled capsule which contains many very small, circular flattish seeds with a central bulge having many small bumps, a little like a flying saucer sweet, but far smaller. They can remain viable in the soil for 10 years.
Liriodendrin is a dimeric furo-furanoid lignan glycoside. One website (probably wrongly) shows it not with two glycosides, but with four). It is also found in Wild Madder and the
Tulip Tree (Liriodendron tulipfera) from which it derives its name. It may have applications as a suppressor of Calcium chloride-induced arrhythmias due to its calcium-channel antagonistic effect in nerve cells.
These two alkaloids are Pyrroloquinazoline alkaloids, both found in Common Toadflax along with several similar derivatives. Peganine, aka Vasicine, was though to have a bronchodilatory effect comparable to that of Theophylline, but it has now been shown that this is false, and exhibits instead the opposite bronchoconstrictory activity! Vasicinone is the 9-ketone and the auto-oxidation product of Vasicine. These alkaloids are known uterotonic, oxytocic and abortifacients. They are also active principles present in the
Harmala plants, which includes
Syrian Rue (Peganum harmala), although chemically they are very different from Harmine, Harmaline and
Harmalol which have the pentagonal ring in the centre.
Quinazoline itself and upon which the above substances are based, is an alkaloid with two nitrogen atoms, shown here only for the purpose of illustration; it has no quoted presence in Common Toadflax.
Quinazoline is isomeric with
Cinnoline which have the two nitrogen atoms in differing positions on the same ring. There is no reported presence of Quinazoline in Common Toadflax.