Australia’s contribution is so significant because it is home to over 20,000 species, about 10 per cent of the world’s total, and contains one in seven globally-threatened species.
The 1000th Australian sample was the rare Acacia Pubescens, known as downy or hairy-stemmed wattle, a plant native to western Sydney which has been threatened by the city’s expansion since World War II.
The scientists do not take just one seed from the Acacia Pubescens and other plants like it.
The average is 32,000 seeds per collection.
They are dried and frozen and stored in a nuclear-proof vault bigger than a football pitch 200m beneath the Sussex countryside, 50 km south of London.
The acacia samples will join seeds from 23,000 other species collected so far from 126 countries in the project administered by the Royal Botanic Gardens at Kew.
"We don’t just lock the door and forget about them," Dr Smith said.
"We test them regularly for viability. Some seeds could last for thousands of years, but others aren’t so fortunate."
Among the less robust are many of Australia’s rainforest plants.
"Nearly 2000 of our rainforest species have seeds that are sensitive to drying out," said Dr Tim Entwistle, executive director of Sydney’s Botanic Gardens Trust, which now has one-third of NSW flora in its seed bank.
"We will have to examine other ways of preserving them, such as cryo-storage."
Like other banks, investors in the Millennium Seed Bank might sometimes make withdrawals.
The Sussex vault, for example, contains six extinct species from Africa which can be reintroduced.
Dr Smith said land use remained the biggest threat to the diversity of plants.
"Clearing of natural vegetation accounts for 20 per cent of carbon emissions – more than the world’s transport emissions – yet we still do it," he said.
"It’s a political problem – it’s something we could stop tomorrow.
"I think a moratorium on deforestation is something the next climate change convention may well look for."
Dr Entwistle said plants affected every aspect of life.
"The air we breathe, the clothes we wear, the food we eat, the furniture we sit on, there’s no part of your life unaffected by plants," he said.
"Each one is a Mona Lisa, a unique product of evolution that has taken effectively 3.8 billion years to produce, and if you lose it you may not get it back again.
"Human beings have been here such a short time, and it’s very courageous tinkering we are involved in.
"We don’t yet understand what uses we may have for many plants.
"Why cut off our options?
Dr Smith is also on a drive for funding to resource the next decade of his seed project to 2020.
He is, in effect, looking for seed money, with long term growth assured.