Not to be confused with :
Burdock [plants of similar name]
When of advanced age, the leaves resemble and are of similar size to those of : Chilean Giant-Rhubarb (Gunnera tinctoria), Brazilian Giant-Rhubarb (Gunnera manicata), Indian-Rhubarb (Darmera peltata), and Rhubarb (Rheum rhubarbarum).
Some similarities to : White Butterbur but that has reduced-width leaves which are more arrow-shaped, and all white flowers. The leaves of Colt's-foot are also similar, but usually smaller, and the marginal teeth on Colt's-foot leaves are shorter in relation to their width, and are also stained reddish when viewed in sunlight.
Slight resemblance to : Winter Heliotrope but that has much smaller and smoother leaves which are evergreen (and thus there all year around unlike Butterbur where the flowers appear before the leaves) and a more open and shorter flower head spike.
Superficial resemblance to : Giant Butterbur but that has much larger and white outer disc florets and yellow inner disc florets; and when young looks like a giant cauliflower.
Uniquely identifiable characteristics
Distinguishing Feature :
Butterbur grows in marshy or damp soil, besides streams and canals, within moist forests or amongst mosses on the ground. The flowers are the first to appear, followed by leaves which get bigger and bigger until when the flower is spent the leaves have grown up to 2 feet across on long stalks up to 3 feet high.
The enormous leaves of Butterbur were once used to wrap butter, hence the name 'Butterbur'. Butterbur is dioecious, meaning it bears male and female flowers on separate plants. The male plant occurring throughout the UK, but the female plant occurring predominantly in the North and Central UK.
The flowers of the male plant are larger (7-12mm) than those of the female plant (3-6mm), but the situation is reverse regarding the height of the plants; the females are taller. It is likely that it is only native where both sexes occur together.
A SESQUITERPENE ALDEHYDE
Lauraldehyde) is contained in the sap and released into the atmosphere from broken stems of Butterbur where it then smells of fresh laundry.
TWO SESQUITERPENE KETONES
Reflecting the structure of the Sesquiterpenoids detailed below are two ketone sesquiterpenes found in the essential oil of Butterbur, Nooketone and Dihydro Karanone. There are others not shown here.
Nookatone is also present in Grapefruits, from which it can be extracted commercially, for it is an expensive aromatic compound used as a fragrance. It is an effective repellent against termites and the sheep ticks that may carry Lyme disease. Ingested, a dose of nootaketone daily stimulates energy metabolism, reducing the significance of a high-fat or high-sugar diet, thus helping stem development of hyperglycaemia. Its non-ketonic analogue is called
Valencene which is contained within Valencia
Dihydro Karanone has a strongly woody, slightly citrus-like fragrance, and indeed it is also found in several
Other compounds present are the sesquiterpenoid glycoside
isoPetasoside and its aglycone (without the attached sugar molecule) the phytotoxin sesquiterpenoid isoPetasol. Petasol and isoPetasol are potentially of use as herbicides. The only difference between Petasol and isoPetasol is the position of the double bond on the side chain. A similar difference applies to the Petasin and isoPetasin (shown below) which are esters of the above sesquiterpenoids. All occur in Butterbur, and from which they all derive their names.
isoPetasin are the main active constituents of Butterbur, but at least 20 other sesquiterpene esters have been identified. The two are double-bond isomers of each other (top right). (There are many differing stereoisomers of these compounds present in Butterbur, too many to detail, and they all have the same chemical formula as those above anyway if not the spatial arrangement. Both Petasin and isoPetasin have pharmacological properties and are effective against migraine. Petasin can also be used to treat allergies.
Two sulfur-substituted Petasins were also discovered in Butterbur, S-Petasin and iso-S-Petasin.
Furano-sesquiterpenoids (or more strictly
Furano-Eremophilanes) echo the structures of the Petasols, but are more poisonous on account of the fused furan ring (the five-membered heterocyclic ring with an embedded oxygen atom) which is easily broken.
Eremophilane Lactone found in Butterbur. Notice the similarity to the two
Furano-Eromophilanes above, but with the major difference being that the ring oxygen has been replaced by a nitrogen atom, meaning that this one is an alkaloid.
The major Pyrrolizidine Alkaloids (PAs) account for 90% of the total alkaloid content of Butterbur. These PA's have the 1,2-unsaturated
Necine structure. The main ones being Senecionine,
Integerrimine and Senkirkine.
The Toxicity of Pyrrolizidines
Most, but not all, Pyrrolizidine alkaloids are hepatotoxic, damaging the liver if ingested in sufficient quantities. PAs themselves show little or no toxicity, it is only in the mammalian liver where they are metabolized to highly toxic alkylating pyrrols but only if their structure includes a double-bond in the 1,2-position of the necine and also has a substituted group on the Nitrogen atom and esterification of the OH-groups of the necine (with mono-esters being less toxic than di-esters). Accordingly, the structure of Tussilagine shows that it is not hepatotoxic.
Tussilagine is a very simple Pyrrolizidine Alkaloid which was discovered in Colt's-foot (Tussilago farfara), hence the name. Tussilagine is one of the few pyrrolizidine alkaloids that are not toxic and does not cause chromosome damage in cultured human lymphocytes.
Integerrimine has a 12-membered di-lactonic pyrrolizidine ring and is pyrrolizidine alkaloid of the retronecine type III kind. It is found in various other plants belonging to the Senecio and many other Genera. It is a geometric isomer of Senecionine, shown below. Integerrimine is anti-mitotic, inhibiting cell division, and induces abortions and fetal malformations in mice. Although it does not induce germ-cell line chromosomal aberrations , it does alter the soma-cell line chromosomes in bone marrow cells.
Senecionine (aka Aureine and Squalidine) is a pyrrolizidine alkaloid which is hepatotoxic, damaging the liver on ingestion, and found in Tansy and also in species of Senecio [in the Daisy Family] (which includes
Ragworts such as Oxford Ragwort, Groundsels) and species of Crotalaria (a member of the Pea Family) which grows in the tropics. Senecionine has uses in the biological laboratory.
Both Senkirkine and
Petasitenine lack the bridging bond across the N-decahedron, thus failing to making them into two fused pentahedra. Senkirkine, which can induce hepatic tumours in rats, also occurs in Colt's-foot.
Petasitenine (below), which was discovered in Butterbur, has an un-stable energetic epoxy group (top left). Compare this structure with that of Jacobine, another pyrrolizidine alkaloid. Petasitenine is also present in Giant Butterbur (Petasites japonicus).
Tussilagine (and its stereoisomer
isoTussilagine) are both also found in Arnica species flowers.