The American oak planted by the then first lady now stands about 22 metres high and is one of the closest trees to the residence of Ambassador John Berry.

The Governor-General was presented with a potted sapling from that tree, prompting her to remark she would have to find the right place to plant it, given its expected height at maturity. She was also given a framed photograph of Mrs Roosevelt's tree planting.

The ceremony at the embassy, hosted by the openly gay ambassador, came just days after Ms Bryce supported gay marriage and as the national capital is about to host the nation's first gay marriages.

Mr Berry and his partner of 17 years, Curtis Yee, a lawyer and native of Hawaii who arrived in Canberra in September, were married recently in Washington DC.

The issue of gay marriage was not mentioned by Mr Berry or Ms Bryce in their speeches and they did not take questions from the media.

Mr Berry said while no one thinks twice now about first ladies making solo trips, Mrs Roosevelt's goodwill tour across the Pacific during World War II was groundbreaking.

There were strong objections to her idea, both from the president and the military.

''Travelling in a war zone, visiting troops in the field and inspecting Red Cross installations weren't the sorts of things that women did,'' he said.

''It took tremendous courage to make that journey - the tide of the war had turned but the Pacific was still a very dangerous place.''

As the first chair of the UN Human Rights Commission, Mrs Roosevelt was instrumental in developing the Universal Declaration of Human Rights.

Mr Berry said Ms Bryce carried on Mrs Roosevelt's tradition of ignoring preconceived ideas about what women should or should not do.

''She, too, is a role model, not just for the women and girls following in her footsteps, but also for people who aspire to be public servants, educators, mentors and leaders,'' he said. ''Today the Governor-General will plant a red box gum - it is a symbolic bookend, arboreally anchoring our alliance for the next 70 years.''

Ms Bryce said she had always loved Mrs Roosevelt, ''the role model of an authentic heroine, a shiny beacon of hope, inspiration and courage''.

''Her books and her biographies are always nearby on my shelves,'' she said.

Ms Bryce said Mrs Roosevelt visited 400,000 troops during her five-week tour, as well visiting factory workers and attending civic receptions.

''An idealist, she sought to move people with her concept of social justice,'' the Governor-General said.

For the lunch at the embassy for Ms Bryce, the Australian War Memorial displayed a flag from its collection which was signed by Mrs Roosevelt during her Australian visit.

The ambassador and the Governor-General met Kerrie Tim, whose mother worked for the American Red Cross in Brisbane during World War II and met the US first lady.

A photograph of her mother with Mrs Roosevelt appeared on the front page of a US newspaper.

Mr Berry told the Governor-General later he was enjoying listening to birds on the embassy grounds.

''One our first day, we opened the bedroom window and I didn't recognise one bird call … the cockatoos are here, and the galahs,'' he said.