One of the trees, Erythrina schliebenii, belongs to the genus of 'coral trees' which have spectacular red flowers and viciously spiny trunks. The tree was only known from two collections from the 1930s until it was recollected in a small patch of unprotected forest in 2001. It was feared that it might have gone extinct again when a Dutch company cleared part of that forest for a biofuel plantation in 2008.
The other tree, Karomia gigas, was only known from a single specimen cut down a few years after it was first discovered in coastal Kenya in 1977. Another tree was found some 600 km away in a tiny fragment of forest in Tanzania in 1993, but a more recent search at the same site was unable to relocate it.
Last year botanists from the University of Dar es Salaam set out to look for both trees near where they had been found. They discovered small populations of both in remote coastal forest near Kilwa in SE Tanzania.
The coral tree Erythrina schliebenii was collected with mature seeds for the first time, allowing taxonomists at the Royal Botanic Gardens in Kew to confirm it as a distinct species. This was only possible through consulting reference collections of coral tree specimens housed in herbaria throughout the world.
Neil Burgess, senior advisor to WWF's conservation and Africa programme, said: "The re-discovery of these two trees highlights the lack of information in a forested region where we could be losing species without ever knowing they are there.
Conservation of these forests, in partnership with local villages, is essential. This can also lead to standing forest being used as an income source for communities through the development of sustainable logging initiatives."
Recent improvements in infrastructure, together with a rapid population increase, are putting the coastal forests of SE Tanzania under increasing threat of being degraded and cleared.
"Erythrina schliebenii has only survived because it grows in rocky areas that are not usually cleared for cultivation but even those areas will be cleared one day if nothing is done," added botanist Cosmas Mligo from the University of Dar es Salaam,
Roy Gereau from the Missouri Botanical Garden, who is a member of the East African Plant Red List Authority and coordinates the collection of data for IUCN Red List assessments in East Africa, said: "Both trees are still in critical danger of extinction, given that fewer than 50 individuals of each species are known."