Key Points:

Having slammed the door shut to working with National a mere three months ago, the Greens now want to reopen it.

How else to interpret Russel Norman's speech last Sunday other than as a plea to National to talk?

The Greens' co-leader's language in the "state of the planet" address - an annual fixture on the Greens' calendar - was pretty direct. He committed the Greens to working with National where the two parties could find common ground and challenged Key to work across all political divides, sharing knowledge, ideas and purpose so the country could ride out the economic storm.

The Prime Minister's response was immediate and positive, inviting the Greens' leadership to a sit-down chat when Parliament resumes next month.

Norman's motives in urging Key to follow "his better instincts" and reach out to parties beyond his Government's official support partners - Act, the Maori Party and United Future - were not entirely selfless.

The Greens' vision remains highly relevant - witness the huge emphasis new US President Barack Obama is placing upon renewable energy and energy efficiency.

However, as a party, the Greens, positioned to the left of Labour and their votes not needed by a centre-right Government, will struggle for relevance as political players.

Their options are to spend this parliamentary term either in ideologically pure but not-so-splendid isolation or roll up their sleeves and co-operate with National and achieve something concrete.

The benefits of the latter for Key are two-fold. First, as Prime Minister, he can do with having some insurance in the event of all of National's support partners refusing to support some piece of legislation which the Greens might back. Even if the Greens only abstained, National would have sufficient numbers to outvote all other parties.

Second, Key is interested in his party building long-term relations with minor parties so that National retains the numbers to govern after future elections.

What was significant was that Norman sought to promote dialogue by listing Green initiatives which National could support. They ranged from the public service being required to buy the most fuel-efficient vehicles to having "smart" electricity meters which would allow consumers to run appliances at cheaper off-peak times, thus reducing the need for new power stations.

That list was a far cry from last year's election campaign when the Greens announced they could not back a National-led Government. That decision followed the Greens' analysis of Labour and National policies in a dozen crucial subject areas ranging from the environment to social policy. In only one policy area - cleaning up the country's waterways - did Labour rate more poorly than National.

The Greens' shift from emphasising the differences to stressing areas where National and the Greens could take "united action" comes a couple of weeks after Nandor Tanczos bluntly described the Greens' pre-election backing of Labour as "fastening your lifeboat to a sinking ship" and a "stupid thing to do".

The former Green MP has long argued the party needs to forge a new political space genuinely independent of Labour and National and which allows the Greens to choose - "genuinely" being the key word. What was new was his accusation that the Greens lack the courage to try.

As Norman noted, the Greens could hardly be part of a National-led Government which cut taxes for the rich and suspended the emissions trading regime.

However, while his speech is a long way short of the territory Tanczos inhabits, it is a step in that direction.