When Grapes Hill Community Garden was built the tarmac that originally covered the site was removed and soil was brought in by truck from a depot on the edge of Mousehold Heath in Norwich. Originally, the soil came from the war memorial site outside Norwich’s City Hall.
With the soil came plants, in the form of roots (Hedge Bindweed, Calystegia sepium, which we fortunately removed in late winter 2011) and seeds. The latter included lots of commoner weeds but also some more interesting exotics, such as Milk Thistle (Silybum marianum), Shoo-Fly Plant (Nicandra physalodes) and Caper Spurge (Euphorbia lathyrsis).
I knew that the bold, upright plant with its rigidly arranged leaves with their white midribs was a spurge (Euphorbia) but it was only recently that I confirmed that it was Caper Spurge (Euphorbia lathyris). It is now starting to flower and, as it is a biennial this will be its last year in the garden. We have option of letting it seed but will probably remove it before then to prevent the garden becoming a forest of its seedlings. The seeds (which look like capers but are very poisonous) are released explosively and are also dispersed by ants (reference). We will need to be careful when removing it, as the toxic, milky sap can cause skin irritation and even serious injury if splashed in the eyes.
Caper Spurge is also known as Mole Plant because it allegedly deters moles where it is planted. Another name is Petroleum Plant because it contains high levels of hydrocarbons, and it has been suggested that it could be used as a petrol substitute if enough of the plant was grown.
Medicinally, Caper Spurge was sometimes used as a violent purgative. Beggars sometimes used the leaves to create unsightly skin sores, which would cause passers by to give them more money out of pity. The excellent Plants For A Future Database lists other uses as well, including the treatment of tumours and snake bites.
There are some good pictures of the plant on the Virginia Tech Weed Identification Guide website if you need to identify it. The plant is classed as a naturalised alien in the UK, on roadsides, waste tips and old gardens as well as in open woodland (view UK distribution map). It is sometimes grown in gardens as well.