> Not so in Australia. The Greens here are left of the Labor Party and many of the more militant unionists support them over Labor.
A friend of mine wrote an essay for Overland on the politics of the Australian Greens which I highly recommend:
http://web.overland.org.au/previous-issues/feature-tad-tietze/
I'm a member of the Greens (but not very active) and I think there are some specific reasons why they're lefter than Green Parties elsewhere. A major one is the unusual preferential voting system, whereby people can vote for minor parties without 'wasting their vote' because it will flow to their second preference. Unlike in non-preferential first-past-the-post systems, this has allowed the party to demonstrate a reasonable amount of support and get some public funding that comes with it, keeping it from being completely marginal. But unlike in proportional systems, it has until this year (they won Melbourne) kept them out of the lower house because they haven't been able to win electorates. So they haven't faced the co-opting pressure of coalition government. Meanwhile they have steadily increased their presence in the Senates (federal and state), which are proportional - but basically review bodies without legislative initiative.
The controls are New Zealand and Germany, with proportional representation. The left of the NZ Greens has mostly been purged or given up, and the party has fallen to the temptation of becoming a centrist 'balance of power' party. Same, as I understand it, in Germany - there's a good analysis by Frieder Otto Wolf in the 2007 Socialist Register: http://socialistregister.com/index.php/srv/article/view/5870
There are powerful centrist forces in the Australian Greens, and a fairly good chance the party will eventually go that way - but it does still feel open to change.
Mike