Repeatedly over the Earth’s history all the land masses have congregated into a single Super Continent. The most recent of these formed at the dawn of the age of the dinosaurs  when the giant northern continent of Laurasia and giant southern continent of Gondwana came together around 300 Million Years Ago (mya). Gondwana split away again around 175mya.                  

As Gondwana, and Laurasia pulled apart the respective landmasses took samples of most plant and animal groups with them. In their relative isolation life would evolve distinctly in the two continents. Around 130mya are the oldest known fossils of flowering plants and they soon spread across both Laurasia and Gondwana. By the time of the Cretaceous–Paleogene extinction event 66mya flowering plants had diversified into most of the orders (the classification level above family) that exist today and started to displace conifers to dominate the worlds flora. 

Not long from splitting off from Pangea  Gondwana itself started to break apart. The chunks that made up Gondwana are today South America, Africa and Arabia, Madagascar, India, Antarctica, Australia, New Guinea, New Caledonia and New Zealand. 

As Gondwana’s fragments drifted apart they took their shared distinctiveness of flora and fauna with them and continued to evolve in distinction to each other after their separation. As some landmasses drifted near to fragments of Laurasia they saw an sudden influx of new species that would alter their ecology, others like Australia and New Zealand, New  Caledonia  would remain in near splendid isolation and keep their weird and wonderful creatures, like the platypus, kiwi and kagu.

From a gardeners point of view the plant group that most readily represents shared Gondwanan heritage is the southern beeches; Nothofagus.                                                            Nothofagus was first described as a separate genus from the northern beeches (Fagus) by botanists in 1850.  The 45 existing species are deciduous and evergreen trees. They grow in Chile, Australia and Tasmania, New Zealand, New  Caledonia and New Guinea. Fossils of Nothofagus have also been found on Antarctica from plants that lived as recently as 3mya and in other parts of Australia and South America that no longer have southern beech forests. The existing species of Nothofagus fit into four distinct groups and it has recently been proposed that they be separated into four genera: “Nothofagus is recircumscribed to include five species from southern South America, Lophozonia and Trisyngyne are reinstated, and the new genus Fuscospora is described. Fuscospora and Lophozonia, with six and seven species respectively, occur in New Zealand, southern South America and Australia. Trisyngyne comprises 25 species from New Caledonia, Papua New Guinea and Indonesia.” - HEENAN, PETER B.; SMISSEN, ROB D. (2013). "Revised circumscription of Nothofagus and recognition of the segregate genera Fuscospora, Lophozonia, and Trisyngyne (Nothofagaceae)". Phytotaxa 146 (1): 131.

How can we know this? Well geologist are clever and canny. Geologists collect rock samples from all over the Earth’s surface and like botanists have identified and classified them. Similar rocks have similar origins and likely arose together in the same place even if they are separated by hundreds of miles today. When new crust is made it emerges as a liquid (lava) and contains small metallic crystals that act like small compass needles before being trapped pointing to the pole as the new rock solidifies. The indicated force lines in these rocks can then be compared with others and with what is known of the shape of the magnetic field at the time to gauge where theses rocks were as they formed.   

There are many other plant families, genera and even some species that grow wild today separated by thousands of miles from each other in the Southern Hemisphere. Gunneras have spread themselves far and wide:

While some plants grow or have close relative across different parts of Gondwana’s constituents others took a Gondwanan ‘seed’ as a jumping off point and have run with it:

Gondwana split in several chunks and is now scattered surrounded by oceans centred around  Antarctica. Around 45- 50mya the South Tasman Rise was breached, isolating Antarctica from Australia and the uninterrupted circum-polar Antarctic Ocean was formed. The now isolated Antarctica became drier and colder as warm, moist air could no longer reach it, loosing all it’s woody vegetation by 3-2mya and it is now largely encased in kilometres thick ice. The Southern  Ocean has strong winds whipping around it constantly with little land mass to slow it or reduce the famously giant waves of the ‘Roaring Forties’ and ‘Furious Fifties’. Land that does descend into the Southern Maelstrom needs plants that are especially tolerant of salt winds and cool, moist conditions. Sounds familiar doesn’t it West Coast Gardeners?! So plants from the coasts of Southern Chile, Tierra del Fuego, Falklands, Tasmania and the South, Stewart and Chatham Islands of New Zealand all experience similar conditions to ourselves with cool summers and mild winters, lots of rain and plenty of wind. As such present us with a panoply of native plants suitable for our gardens.