Mampela Ramphell and Helen Gill said they represented South African unity.
An agreement that would have given South Africa's main opposition party, the Democratic Alliance (DA), a black presidential candidate has collapsed.
Under last week's agreement, the DA was to merge with the Aghan party, led by anti-apartheid activist Mampela Lampele.
Ms. Runfel had been recommended as the Democratic presidential candidate for this year's election.
The combined party had been touted as the strongest challenger to the ANC since it came to power in 1994.
Ranphell was the partner of Steve Biko, one of the veterans of the struggle against white minority rule, who died in police custody in 1977.
Despite optimism when the Aghan Party was launched in Pretoria in June 2013, the party has not made an impact
Supporters of the DA hope Mr Ramphell will help the party tap into voters' dissatisfaction with President Jacob Zuma and the African National Congress (ANC), which has come under fire for corruption scandals and still high poverty levels. I was expecting.
The short-lived union was billed as a historic change in South Africa's political landscape, as it was the first time the Crown Prosecution Service fielded a black presidential candidate.
Analysts say the bill has failed to make significant progress among the majority of black voters, amid accusations that it is a vehicle for white interests.
However, the merger broke down at a meeting on Sunday over whether it would be a mere partnership or a complete assimilation with the much smaller Agan.
“Dr Ramphell has broken the agreement under which she ran as a presidential candidate in the state assembly and that Aghan SA branches, members and volunteers would be incorporated into the state assembly,” state assembly leader Helen Gill said in a statement. .
She angrily accused Mr. Ramfel of saying one thing to the media, another to Agan's supporters and even to the prosecutors.
“Dr. Ranfel has proven once and for all that she cannot be trusted to see any project through to completion,” she said.
However, Ramphell responded on Twitter, insisting: “There was no disruption. I am committed and am still the leader of Aghan SA. The focus was on working together in the elections.”
On Friday, the DA issued a joint statement announcing that Mr. Lunfel would be joining its ranks. The DA's rules state that only its members can be candidates under its banner.
Ms Ranphell said the statement was issued without her consent and that she would remain Aghan SA's leader.
Mampela Ramphel, 66, launched her own political platform, Aghan, a year ago, but it has not made much of an impact. She is currently bankrupt and was unable to pay her employees a month ago.
“We will remove the excuse of race and challenge the ANC to be judged on its performance,” she said when the deal was announced.
“We take that race card and throw it in the trash.”
But the ANC claimed prosecutors were taking advantage of her because of the color of her skin.
ANC secretary-general Gwede Mantashe said: “This is a rented leader, a rented black face.”
No date has been announced for the general election, but it could be held as early as April, 20 years after the first democratic elections that ended decades of white minority rule.
The president is elected by members of parliament, so candidates must win a majority in parliament to ensure that a party will lead the country.
Ranphell, who worked as a community doctor in the Eastern Cape with Steve Biko, led a grassroots resistance movement against white minority rule in the 1970s.
She has since served as a director of the World Bank, vice-chancellor of the University of Cape Town, and until recently served as director of a major mining company.
Agang is named after the Sesotho word meaning “Let's build.”
