For a party that elected a leader for the first time less than six years ago, Sargent has no shortage of ambitious potential successors. A case can be made for any of the six parliamentary party members as next leader.

Dan Boyle, likely to be appointed to the Seanad in the coming weeks, would certainly have been in the shake-up were he still a TD. And the possibility of a challenge from another high-profile Green who is not in the parliamentary party . . . Patricia McKenna, Niall O Brolchain or Deirdre de Burca . . . cannot be ruled out.

However, Sargent's successor is likely to be one of three senior party figures: new environment minister John Gormley, new energy minister and one-time presidential hopeful Eamon Ryan, or deputy leader Mary White.

Sargent aside, the other two TDs - Ciaran Cuffe, who is close to Ryan, and Paul Gogarty - would be seen as more likely candidates to be the leader after next.

Of the three favoured candidates, Gormley would be regarded as a slight front-runner. He is party chairman; he has ten years' experience as a TD; he was the first Green mayor in 1994; and he has twice seen off no less a politician than Michael McDowell to take a seat in Dublin South East.

On experience alone, he has a serious chance.

Eamon Ryan is probably the party's most charismatic and polished performer, particularly on television where he regularly excels as a thoughtful and reasonable contributor. He would be on the 'Realos' wing of the party . . . although, after last week, it's a moot point whether any of the parliamentary party could now be called 'Fundis' . . . and many commentators believe he would be best placed to increase the party's appeal outside its core support.

However, the way Ryan handled the party's on-off bid for the presidency in 2004 didn't endear him to everybody in the party.

There was some irritation about the way he put himself forward, while others were disappointed that he didn't go the whole way and contest the election against Mary McAleese.

But that was three years ago, and nobody in the party doubts that he is a serious asset to the Greens . . . plus he has long been considered a likely successor to Sargent.

Asked about the leadership on Wednesday night on RTE Radio One's Tonight with Vincent Browne, Ryan said he did not think he would run. Given his elevation to cabinet, he may prefer to concentrate on his new ministerial duties. But he would certainly have his admirers in the party and cannot be ruled out at this point.

The dark horse in the race could be new Carlow-Kilkenny TD Mary White. Unlike other political parties, the Greens are keen on the idea of sharing responsibility and the party does put a huge emphasis on gender balance. If there is a view in the party that Gormley or Ryan have enough on their plates with their new positions, White as deputy leader would certainly come into the picture, although she does not have anything like the national profile of the two new ministers.

The real nightmare scenario for the party would be if four or five people put themselves forward as candidates, prompting a potentially divisive and distracting campaign with the party, in the words of one source, "washing its dirty laundry in public". Coming within a couple of months of finally crossing the rubicon and entering government, that would be a PR disaster for the Greens who need to focus all their attention on their new responsibilities.

For that reason it is believed that efforts will be made among senior figures in the party to come up with an agreed candidate, in the same manner as the PDs did last year when Michael McDowell was appointed leader without a contest.

But there will be an argument from others in the party for some form of contest, and the possibility of somebody disaffected by the decision to enter government laying down a marker by contesting for the leadership . . . even if he or she has no chance of success . . . can't be ruled out.

While nominations will probably be required by July, such a contest may not take place until as late as September, although a new leader could be in place much sooner if a compromise candidate can be agreed.

Assuming that outgoing leader Trevor Sargent is a banker for the party's junior ministry . . . which will probably be in agriculture, with responsibility for food and horticulture . . . the other decision the Greens will have to make in the coming days is who will fill the party's two spots in the Seanad as the taoiseach's appointees.

Dan Boyle will certainly be one of the two, with Deirdre de Burca of Wicklow, Galway West's Niall O Brolchain and Dundalk-based Mark Deary seen as the most likely candidates for the second place.

De Burca, having come closest to being elected last month, is probably a slight favourite and her nomination to the Seanad would also be attractive to the party on gender balance grounds.

However, O Brolchain will be optimistic about taking Labour's seat in Galway West at the next general election, while Louth could well be a five-seater, giving Deary a realistic chance of targeting a seat there.

In recent days, party headquarters has been receiving abusive phone calls and resignations over its decision to enter government with Fianna Fail and the PDs, but the huge endorsement of the decision by 86% of delegates on Wednesday night has reassured the leadership that there is little possibility of a sizeable anticoalition rump forming. The party will certainly need to stay united over the next five years.