“Governing is about making compromises,” Mr. Laturi said. When the Finnish center-right government recently announced it would build two new nuclear plants, the Greens opposed it but did not resign. “It was a free parliamentary vote. We voted against the new plants but decided to remain in government. It is more effective than being in opposition,” Mr. Laturi said.

The Greens in Germany made many compromises when they joined the federal government for the first time, in 1998, under Chancellor Gerhard Schröder, a Social Democrat.

During their seven years in the coalition, the “realos,” the realist wing of the Greens, prevailed while the “fundis,” or fundamentalists, who were committed to pacifism, state interference and higher taxes to finance ecological and social policies, were marginalized.

The Greens supported the NATO bombing of the former Yugoslavia in 1999 to stop the Serb policy of ethnic cleansing of Albanians in Kosovo. In 2002, they agreed to send German troops to Afghanistan. They moved so much to the center that they supported Hartz IV, Mr. Schröder’s radical reforms of the social welfare system designed to encourage the unemployed to re-enter the labor market by reducing certain welfare benefits.

Out of office since 2005, the party has shifted leftward.

It wants the German troops pulled out of Afghanistan. It has proposed more state spending and higher taxes. And when Mrs. Merkel’s coalition decided this week to raise the monthly Hartz IV unemployment benefits by €5, higher than the increase pensioners will receive, the Greens protested. Not only did they distance themselves from their own previous policies, they demanded a hefty increase for the unemployed, even though a majority of Germans oppose such a move: taxpayers will have to foot the bill. It is the realists who are now marginalized, said analysts.

Because of this move to the left, the Greens are profiting. It is a paradox because of the party’s economic base.

Reinhard Bütikofer, a leading German Green member of the European Parliament, said his party “represents a certain lifestyle.” Green members are better educated; around 60 percent of members are university graduates, compared with 15 percent for the two biggest parties, the Christian Democrats and the Social Democrats.