German Chancellor Angela Merkel's conservatives will Thursday meet the Greens party for initial coalition talks, sounding out an alliance that is seen as unlikely but not impossible.

The exploratory talks with the left-leaning ecologist party are part of Merkel's hunt for a governing partner after her conservatives won September 22 elections but fell short of a ruling majority.

Merkel's Christian Democrats (CDU) and their Bavarian partners the CSU are already engaged in talks with the centre-left Social Democrats (SPD), who are widely seen as the more likely ally.

But -- should those talks fail or SPD rank-and-file members revolt against a 'grand coalition' deal -- Merkel could surprise voters by seeking to team up with the party the CDU long deemed radicals.

However, doubts seemed to outweigh optimism Thursday about such a new odd couple, as veteran Greens politician Juergen Trittin criticised the Merkel government.

He spoke of "clear conflicts" between them in energy, climate and eurozone policy and labelled CSU Interior Minister Hans-Peter Friedrich's comments on tougher rules for asylum seekers "an abyss of cynicism" after the migrant deaths on the Italian island of Lampedusa.

Only days ago, Environment Minister Peter Altmaier had told news magazine Der Spiegel that "the chances of a coalition with the Greens have risen in recent days from 'theoretical' to 'conceivable'".

The Greens' new duo of leaders, Katrin Goering-Eckardt and Anton Hofreiter, said Wednesday they were willing to talk but remained sceptical, vowing to stick to their guns on the values they hold dear.

"We want to keep fighting for a more ecological, just and modern country," said Hofreiter.

The Greens, who grew out of the environmentalist, anti-war and anti-nuclear movements, entered parliament in the 1980s, many wearing sneakers and long hair and handing out sunflowers.

But what started as a protest party has become increasingly mainstream as German society has turned greener.

Many of the Greens' demands, such as greater rights for gays and lesbians and immigrants, are now widely shared, at least in theory. Millions now recycle their garbage, shop organic, ride bicycles to work and have solar panels on their roofs.

The Greens have already had a stint in government, with the SPD from 1998-2005, during which the once avowedly pacifist party signed off on Germany's military deployment to Afghanistan.

Merkel in 2011 adopted the Greens' core demand of a nuclear phase-out, reacting to the public mood after Japan's Fukushima disaster.

The chancellor has already ruled with two coalition partners: the SPD and the pro-business Free Democrats (FDP) who crashed out of parliament in the last election.

Some observers say that the famously pragmatic and non-ideological Merkel may be tempted to woo a third partner, the Greens, in her third term -- although the alternative view says she would prefer a far more stable coalition with the SPD.

An Emnid institute poll found 46-percent support for a grand coalition and 22-percent backing for a conservatives-Greens tie-up. However, asked which scenario was more likely, 79 percent named a grand coalition and only nine percent an alliance with the Greens.

Either way, the CDU has signalled it is serious about talking to the Greens, not just playing them against the bigger SPD to gain leverage.

The Greens, meanwhile, are badly torn about a power pact with Merkel, which the party's "fundamentalist" wing regards as the ultimate betrayal of Green ideals.

The party's "realist" wing argues that a stab at power will let the Greens realise at least some of their goals -- especially correcting the energy transition, which it argues is coming off the rails under Merkel.

Leftist columnist Jakob Augstein wrote that the talks could lead to "a completely new covenant" in German politics that would mean that "the children lost in the turmoil of 1968 return to the bourgeois lap".

"It would be an event of historic proportions," he wrote. "And the end of the Greens."