Australia and New Guinea are portions of the ancient supercontinent of Gondwana, which started to break into smaller continents in the Cretaceous period, 65–130 million years ago. Australia finally broke free from Antarctica about 45 million years ago. All the Australasian lands are home to the Antarctic flora, descended from the flora of southern Gondwana, including the coniferous podocarps and ''Araucaria'' pines, and the broad-leafed southern beech (''Nothofagus''). These plant families are still present in Papua New Guinea. New Guinea is part of the humid tropics, and many Indomalayan rainforest plants spread across the narrow straits from Asia, mixing together with the old Australian and Antarctic floras. New Guinea has been identified as the world's most floristically diverse island in the world, with 13,634 known species of vascular plants.