"This is now the great mystery of Brazilian politics: what will Marina do?" "Marina" is Marina Silva, leader of Brazil's Green Party, and the speaker, Altino Machado, is a journalist and one of her oldest friends. But Marina has already done something remarkable: she persuaded one-fifth of Brazil's voters to support the Green Party.

Twenty percent is the second-highest share of the vote ever won by any Green Party anywhere. (The record-holder is Antanas Mockus, the Green candidate in the recent election in Colombia, who got 27 percent of the vote.) But Brazil, with more than 200 million people, is the country that really counts in South America, and what has happened there is, in the words of the Rio de Janeiro paper O Dia, a "green tsunami."

Among other things, this remarkable result makes Marina Silva the king-maker in the second round of the Brazilian election. It was the votes that went to her that deprived Workers' Party candidate Dilma Roussef of victory in the first round of voting on 4 October. To win in the first round, a candidate must get 50 percent of the vote; "Dilma" ended up with 46.9 percent.

So now Marina (they are both known by their first names) must decide whether to tell her supporters to vote for Dilma in the second round of the election on 31 October, or to give their votes to the relatively conservative runner-up in the first round, Jose Serra. Greens are generally assumed to be on the left, but it is not a foregone conclusion that Marina will back the Workers' Party candidate.

Marina Silva has the classic biography of a Brazilian left-wing hero - born in the Amazonian state of Acre, the daughter of rubber-pickers, illiterate until she was sixteen - but she is also an evangelical Christian. As such, she is fiercely opposed to abortion, and a substantial portion of her vote came from Christians who were horrified by Dilma's advocacy of reform in Brazil's stern anti-abortion laws.

As a social conservative, Marina might even try to throw her votes to Serra. She is wringing every drop of drama out of the situation, and won't announce her choice until a special party convention late next week.

However, her decision matters less than it seems: Dilma only needs a few million extra votes to cross the 50-percent barrier, and Marina cannot really compel all the Greens to vote for Serra. The headline story is still the rapid economic growth Brazil has enjoyed under outgoing president Luiz Inacio "Lula" da Silva - and, just as importantly, the way the new wealth has been shared out.

Fifty million Brazilians have been rescued from poverty (an income of less than $82 per month) by Lula's "family plan" of subsidies for the very poor, and 25 million other low-income Brazilians have actually ascended into the middle class. So Lula leaves office after eight years with a stratospheric approval rating of 80 percent.

He is so popular that he could choose a complete nobody as his successor and get him or her elected. Dilma Roussef is much more than that - a former guerilla during the military dictatorship of 1964-85, a skilled administrator, and Lula's former chief of staff - but nobody has ever accused her of having too much charisma.

No matter. She'll win the second round anyway. What's really interesting here is the emergence, two decades after the restoration of democracy, of what you might call Brazil's political personality.

All three big political parties, the Workers' Party, Serra's Social Democrats, and the Greens, are on the left in terms of economic policy, though Marxist ranters are scarce in all of them. Social conservatives are still well represented in the latter two parties, but they all promise to continue Lula's wonder-working brand of pragmatic socialism. Together, they got 98 percent of the vote in the elections on 4 October.

The rapid rise of the Greens is linked to Brazilians' growing awareness that they are the custodians of the world's largest tropical forest, the Amazon, and that it is in serious danger from global warming. That may explain why 85 percent of Brazilians think that climate change is a major problem, while only 37 percent of Americans do.

It's a striking picture. Brazil is the only one of the BRICs, the big countries with high economic growth rates, to have both a powerful industrial sector (like India and China) and self-sufficiency in energy (like Russia). By the time it hosts the Olympic Games in 2016, it will probably have the fifth-largest economy in the world.

It is still one of the world's most unequal countries, with a gulf between rich and poor that makes even the United States look egalitarian. (20,000 families control 46 percent of Brazil's wealth, and one percent of land-owners own 44 percent of all the land.) But it is moving in a different direction now, without any of the doctrinaire excesses that usually mar such efforts.

In fact, Brazil is becoming not just an important place, but a very interesting place.