Approximately 200 million years ago, there existed a very large, southern supercontinent, Gondwana. This continent contained land areas that would eventually fragment and form South America, Africa, Madagascar, India, Antarctica, Australia, the southern part of New Guinea and New Zealand.

Due to stresses in the earths crust, Gondwana began to break apart during the following 80 million years, and at about 120 million years ago, only Australia and Antarctica remained closely linked together. Subsequently, about 60 million years ago, Australia began a slow movement northwards.

The slow fragmentation of Gondwana meant that the ancestral forms of many plants and animals were able to move from one fragment to another while the distances across water were still small. As a result, Australia, South America, New Zealand and southern Africa have a number of derived animal and plant families in common; India which broke away much earlier seems to have a more distinctive biota. Examples include the ratites (flightless birds) which produced the rhea in South America, the ostrich in Africa, the emu in Australia, the cassowary in Australia and New Guinea and the moa in New Zealand. Marsupials are found in both Australia and South America.

Plants also had common ancestral forms in these various continents. The Proteaceae (Grevillea, Banksia, etc.) are found today in Mexico, central and South America, Africa, southern India, eastern and South-East Asia, Malesia, Australia, New Zealand, New Caledonia and Fiji. The beech family (Fagaceae) includes the genus Nothofagus, which also has a southern distribution. Today, species of Nothofagus are restricted to South America, Australia, New Zealand, the mountains of New Guinea and New Caledonia.

Antarctica has none of these plants or animals as it is now too cold for their survival. Fossil records show, however, that Antarctica once had forests of Nothofagus spp. (beech) and that other plants and animals were present which support the Gondwana hypothesis.

It is very difficult to account for the fungi in the fossil record. Fungi do not generally fossilise well; the fruiting structures are too soft. That fungi were present 200 million years ago is certain, because while the fruiting structures do not fossilise, plant cells clearly exhibiting fungal hyphae within them are commonly found as fossils.

Possible answers to the fungal history of Gondwana come from observations on fungal distributions on the modern continents. For example, the parasitic genus Cyttaria is only found on species of Nothofagus (beech), and has a similar disjunct southern distribution. It is very tempting to suggest that Cyttaria was carried with its host as it spread across Gondwana and eventually became isolated as the continent fragmented.

The beech-associated fungi provide a tiny window through which some idea of the fungi of Gondwana can be obtained. If a fungal species or genus is found in association with the beech forests of Australia, New Zealand and South America, then it is possible that its ancestral forms were also present in the beech forests of Gondwana. One such genus is Descolea which occurs in all three locations and is mycorrhizal on beech roots.

 

Further Reading

Hill, R.S., Truswell, E.M., McLoughlin, S. & Dettmann, M.E. (1999), Evolution of the Australian flora: fossil evidence, Flora of Australia, 2nd edn, 1: 251320.

Morley, B.D. & Toelken, H.R. (1983), Flowering Plants in Australia. Rigby, Adelaide.

Truswell, E.M. (1996), The fossil record of the fungi in Australia and the Australasian region, Fungi of Australia 1A: 321340.

White, M.E. (1998), The Greening of Gondwana, 3rd edn. Kangaroo Press, Sydney.