Not to be confused with : Great Butterwort [a plant with similar name]
Some similarities to :
Cauliflower and White Butterbur when small, but grows much taller than either.
Uniquely identifiable characteristics
Distinguishing Feature :
When small it resembles a cauliflower, but grows to 1m when mature, with several stubby and broad pale-green leaves (actually bracts) emerging at intervals from a stout pale-green stem. The flowers are cream to white, and when fully grown are presented in clusters rather like an 'umbel' at the top of the stalk, quite un-like the spike of flowers on the otherwise similar Butterbur. The flowers themselves (with their 5 white petals) more resemble the flowers of a white-flowered specimen of Butterbur rather than those of White Butterbur.
Can be grown as a garden plant. Grows on wet soggy ground. Occurrence is sporadic across the UK as shown by the distribution map, with a slight preference for the SE. It is a non-native invasive plant which shades out competing plants. First arrived in the UK as a horticultural plant in 1897 it escaped in 1924 and has been spreading ever since. It spreads by underground rhizomes in damp or wettish places along the sides of streams, along roads, in plantations and in both open and shady places. Like Butterbur and Colt's-foot the large kidney-shaped leaves which shade out competing species only form later in the season when the plant is up to a metre high. Like Butterbur and Colt's-foot, it flowers very early in the season, from about mid-January to April; the giant leaves only forming afterwards when other plants would like to start growing.
All Butterburs including this one are dioecious, with male and female flowers appearing on separate plants.
FURANO-SESQUITERPENOIDS / BENZOFURANONES
Furanoligularenone is a Benzofuranone and an Eremophilane (or more strictly a Furano-Eremophilane) found in a few members of the Daisy & Dandelion Family of plants, including Giant Butterbur. It has anti-inflammatory effects.
Furanofukinol is another Benzofuranone and Furano-eremophilanes which is found in the rhizomes of Giant Butterbur. Furanofukinol gains its unusual name from the name of the plant in Japan; Fuki, where it is native and used as a vegetable (after pre-treating with baking soda and soaking in water, which removes most of the astringency and poisonous pyrrolizidine alkaloids.
Two other Furano-eremophilanes occur in Butterbur, (Petasites hybridus).
Petasitenine (aka Fukinotoxin) (not to be confused with Petasinine, which is another much simpler pyrrolizidine alkaloid) is a pyrrolizidine alkaloid isolated from the young flower stalks of Giant Butterbur and is poisonous, resulting in necrosis, haemorrhage and proliferation of bile ducts within the liver of laboratory test rats after drinking a 0.05% solution of this alkaloid, which was their drinking water. They all died. Of those drinking a weaker 0.01% solution only 2 out of 10 animals died within 160 days, developing tumours in the liver. The high toxicity is probably due to the energetic 3-membered ring epoxy group. Petasitenine is also present in Butterbur (Petasites hybridus)
[Note that one dictionary of substances has the methyl group at the middle-top attached instead to the carbon atom just right of the three-membered O-ring - which is probably in-correct - most other sources place it as shown here]