Brazil's former environment minister Marina Silva took another big step on Sunday toward an expected presidential bid by joining the Green Party, which wants to field her in the 2010 race.
Silva, an internationally renowned defender of the Amazon, shook up Brazil's political landscape last month when she said she may run for the country's top job.
"I feel honored with the invitation to run for the presidency and that people embraced the idea," Silva told party leaders and supporters in Sao Paulo.
"But we'll take that decision only in 2010," she said, amid chants of "Marina for President".
Earlier this month, she abandoned President Luiz Inacio Lula da Silva's ruling Workers' Party, or PT, which she had helped found 30 years ago.
The soft-spoken Silva suggested she didn't want to burn bridges but find common ground around the environment issue.
"I'm leaving to build a new house, maybe on the same street," she said, referring to her departure from the PT.
Her candidacy could divide the pro-government vote and undermine the election chances of Lula's chosen successor, his chief of staff Dilma Rousseff.
Silva and Rousseff would both vie for left-wing and female voters, but most analysts believe the race is still likely to be dominated by Rousseff and Sao Paulo state Governor Jose Serra of the opposition PSDB party.
During her half hour speech on Sunday, Silva referred to her friend, the legendary conservationist Chico Mendes, and other figures from civil rights movements, such as Martin Luther King and Nelson Mandela.
Silva, 51, returned to her seat in the Senate when she resigned as environment minister in May 2008 citing opposition within the government to her environmental agenda.
Although she could siphon off votes from Rousseff, Silva's lack of name recognition, access to television advertising or a strong track record means she will struggle to compete, analysts say.
Voters may also have concerns about her past health problems. The former rubber tapper who worked her way out of poverty as a maid has had hepatitis, malaria and metal poisoning. She was hospitalized on several occasions, even as environment minister.
Silva trailed a distant fifth with 3 percentage points in a survey by polling firm Datafolha released earlier this month, which showed Serra in the lead with 37 points and Rousseff in second place with 16.
The Green Party, long a fringe party in Brazil with little clout, made headlines last year when its candidate, Deputy Fernando Gabeira, nearly won the mayorship of Rio de Janeiro.