The sisters had to decide who they would stay with. Some relatives were separated, and it was a painful time.
Mary MacKillop was heartbroken, and lost some of her people. The two groups adopted different habits, names and emblems.
But they pursued the same work - mainly in education and welfare and with women and children in poor and isolated places in New Zealand and Australia.
The two orders started having more contact in the 1960s, when the women were older and not so busy. They really came together in Rome in 2010, when their founder, Mary MacKillop, was made a saint. For the last four years they've debated becoming one again, and four out of five centres decided to do so.
Former "black Joes" are to let go of their emblems at a special mass held at 11am today at St Mary's Church. They will take on their former emblem, and all the sisters have adopted a bright blue scarf as a symbol of their unity.
The choice of blue for a scarf colour amused the bishops, Sister Anne Derwin said. It was for feminine and not spiritual reasons - the blue looked good with any skin colour.
The sisters will follow that ritual mass with a lunch for themselves and 350 invited guests at Wanganui Racecourse.
Tomorrow, there's another mass at St Mary's, this time at 9am and shared with any member of the public. After it the sisters are putting on a morning tea at 10am, for anyone who wants to join them.
Many of them leave Wanganui again after that, for parts as far away as Ireland and Peru. For those who stay there will be a heritage bus tour to places important to the Wanganui sisters. Places include the wharf where they landed in 1880, Heads Rd Cemetery, their first convent site in Victoria Ave, the site of their former Sacred Heart College, their current base at Mt St Joseph and Kaiwhaiki Marae.
The order had a long relationship with the marae. Its people are to provide afternoon tea and entertainment for the tour group.
The Sisters of St Joseph of the Sacred Heart now number 874 worldwide, and their average age is in the 70s. They will disperse to carry on their work in chaplaincy, facilitation, pastoral care, counselling and spiritual direction.
They own everything in common . Leaders say the fusion is already giving them new energy and widening their horizons.