Key Points:

Jeanette Fitzsimons' decision to retire from the leadership of the Green Party in mid-year signals the end of an unconventional political career. In any other party, her outstanding qualities - high intelligence, intense application to problems and solutions, fairness, integrity, compassion, always civilised in debate - would have ensured her senior ministerial positions.

But Jeanette Fitzsimons would not be in any party. She was an environmentalist before she was a politician and left academic life only to further the cause. As the founding co-leader of the Green Party she, perhaps more than anyone in the party, has kept it out of close coalitions that would have given her ministerial positions but would also have required compromises from the party and associations it might regret.

Whether her purity has been good politics is a matter of argument. The Greens have been in Parliament for 14 years and have not much to show for it. Positioned to the left of Labour on economic as well as environmental policy, they never won enough seats to demand Labour's attention until well into its third term. At that point, governing policies on climate change, transport, thermal-power generation and emissions trading began to take on a greener tinge but the tide was going out. Labour could have done without a Green MP's anti-smacking bill.

But Jeanette Fitzsimons could point out that parties more power-hungry than hers are no longer in Parliament. The Alliance went into coalition in Labour's first term, ruptured and disappeared at the next election. New Zealand First, too, had split in coalition with National and narrowly survived to form a third-term partnership with Labour. Now it has gone.

The Greens have survived and have done so on the basis of nationwide support, not reliance on a single electorate as the parties of Jim Anderton, Rodney Hide and Peter Dunne do. Jeanette Fitzsimons won the Coromandel seat for a term and could not hold it, but the party's vote nationwide has been sufficient to keep it in play.

Jeanette Fitzsimons and her initial co-leader, the late Rod Donald, built a party that seems to have a durable appeal not just for its environmental idealism but for the collegial, almost non-political, style of its organisation and campaigning. It has "co-leaders", quaintly of each sex, and gives its MPs room to pursue their own priorities. Sue Kedgley has her food safety campaign, Sue Bradford her concern for the welfare of beneficiaries, Keith Locke his suspicions of security services.

A party of disparate and loosely disciplined interests was held together by the complementary characteristics of Jeanette Fitzsimons and the more forceful Mr Donald. She had intended to retire at the last election but, after Mr Donald's sudden death, decided to stay on, perhaps because his replacement, Russel Norman, possessed many of his tactical skills but lacked his redeeming charm.

Now the Greens need to find a female co-leader as presentable in her own way as Jeanette Fitzsimons. The first to declare their candidacy are Sue Bradford and another MP, Metiria Turei, who is practically unknown to the public. They have several months to press their claims before the party's annual meeting at the end of May.

A change of leader is also an opportunity for the party to review its political approach. The last election has changed the scene somewhat. National's all-embracing leader has brought the Maori Party into his ministry and the Greens want to talk to him too. Their cause is harder to promote in a recession. They need a voice as respected as Jeanette Fitzsimons and capable of compromising when it counts.