Gondwanan flora

The deep history

Gondwana was the southern half of the supercontinent Pangaea — the unified landmass that included present-day South America, Africa, Antarctica, Australia, the Indian subcontinent, and several smaller fragments including New Zealand, Madagascar, and New Guinea. Gondwana began breaking apart in the Jurassic, around 180 million years ago, with the separation accelerating through the Cretaceous and continuing into the Cenozoic. The Indian subcontinent rifted away from Africa-and-Antarctica around 130 million years ago and collided with Asia around 50 million years ago. Australia-and-New-Zealand separated from Antarctica between 80 and 60 million years ago. South America separated from Antarctica around 35 million years ago.

Plant lineages already present on unified Gondwana were carried apart on the drifting fragments. Some lineages — the Proteaceae, the Nothofagaceae (southern beeches), the Podocarpaceae, the Restionaceae, the Cunoniaceae — survived on multiple fragments and continued to evolve in isolation. The result is a recognizable “Gondwanan signature” in the modern floras of the southern continents that does not match anything in the Northern Hemisphere.

The principal Gondwanan plant families

• Proteaceae — Protea, Leucadendron, Leucospermum (South Africa); Banksia, Grevillea, Hakea, [[macadamia|Macadamia]], Telopea (Australia); Embothrium (Chile); Knightia, Toronia (New Zealand). The family is almost entirely Gondwanan; its presence on every southern fragment is one of the clearest pieces of biogeographic evidence for continental drift.
• Nothofagaceae — the southern beeches. Nothofagus species form the dominant forest of much of southern Chile, Argentine Patagonia, Tasmania, the New Zealand cool-temperate uplands, and New Guinea. Fossil Nothofagus pollen is widespread in Antarctica.
• Podocarpaceae — the southern conifer family. Podocarpus, Dacrydium, Phyllocladus, Dacrycarpus, Manoao (the New Zealand silver pine), Lagarostrobos (the Tasmanian Huon pine). Some of the world’s longest-lived trees are Podocarpaceae.
• Restionaceae — the southern “rushes,” dominant in the Cape Floristic Region and southwestern Australia.
• Cunoniaceae — woody trees and shrubs with Gondwanan distribution across South America, Africa, Madagascar, Australia, and New Zealand.

What it tells us

The Gondwanan flora is one of the most direct biological demonstrations of plate tectonics. The 19th-century plant geographer Joseph Hooker noted the similarities between the floras of Tierra del Fuego, southern New Zealand, and Tasmania long before continental-drift theory existed; his observations were one of the empirical puzzles continental drift later explained. The 20th-century recognition that fossil Glossopteris (Permian seed-fern) pollen was distributed across South America, southern Africa, Antarctica, India, and Australia at exactly the latitudes a unified Gondwana would predict was decisive evidence in the eventual acceptance of plate tectonics in the 1960s.

For practical biodiversity work, the Gondwanan signature explains why southern-hemisphere endemics are so often unrelated to anything in the Northern Hemisphere — the lineages have been evolving on separate continents for tens to hundreds of millions of years.

See also

Auto-generated from this entry’s typed relations: frontmatter, grouped by relation type so the editorial signal isn’t flattened.

• Demonstrated by: [[cape-floristic-region]] · [[macadamia]]

Sources

• Cracraft, Joel, “The biogeography of Australian birds and the Gondwanan origins” (multiple papers, 1980s–2000s)
• Sanmartín, Isabel & Ronquist, Fredrik, “Southern Hemisphere biogeography inferred by event-based models” (Systematic Biology 2004)
• Wikipedia — Gondwana, Proteaceae

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A concept entry in the 0mn1.one wiki.