The Green Party effectively began life after a Coventry couple got a group of friends together to discuss a Playboy article on rainforest destruction.
The Greens have two principal speakers instead of one leader
Out of that 1973 meeting a small party called People was born which fielded just five candidates in the February 1974 general election.
The following year People became the Ecology Party and adopted the "Manifesto for a Sustainable Society".
The document would eventually become the "philosophical and policy" blueprint for the Green Party which came into being in 1985.
The organisation describes itself as a "radical party which places social justice, sustainability, local economy, and - of course - the environment, at the heart of its policies".
Funded by its own membership, the Greens have opted to date not to have a leader, instead they have two principal speakers - currently Caroline Lucas MEP and Keith Taylor.
The Scottish Greens have seven people at Holyrood
Despite being hampered by the first past the post system the party has managed to build a respectable representation at local level.
In 1989 they won 14.9% of the vote at the European elections but failed to secure a single seat.
A decade later, voting for the European Parliament had been changed across the UK to a proportional system and the Green Party won two seats and retained them in 2004, polling more than a million votes.
Currently the party also has 63 councillors, one Green peer and two members of the London Assembly.
They are targeting several UK seats for the first Green MP, although without proportional representation it could prove an uphill battle.
The Scottish Greens were founded as the Scottish Ecology Party in 1979 as part of the main UK Ecology Party.
In 1990 the Scottish Green party became a separate party from the Greens in England and Wales, and produced its own manifesto "Towards a Green Scotland".
Although the party shares campaigns and ideas withe the Greens south of border, some policy differences have emerged (for example on the EU constitution, which the Scottish Greens will support but the English Greens oppose).
The party has had some success under the proportional representation system used for the devolved Scottish Parliament.
Robin Harper as the first Green Parliamentarian in the UK in the first Scottish elections of May 1999.
And the Scottish Greens now have seven members of the Scottish Parliament, with 6.9% of votes cast in the 2003 Scottish election.