Botanic Gardens Trust, Sydney, Australia

Proteaceae - evolution

Dr Peter Weston - Senior Principal Research Scientist

In my research I am trying to reconstruct the evolutionary history of the plant family Proteaceae using information from DNA sequences. The Proteaceae is mainly confined to landmasses that once formed the ancient supercontinent Gondwana. The ancestors of most living species of Proteaceae were thought to have ‘drifted’ with the continents. My results support the ‘drift’ of groups found in Australasia and South America. However, surprisingly, some of the South African Proteaceae probably got there much later by seed blown across the Indian Ocean. This emphasises the importance of Australia as a refuge for the descendents of ancient lineages.

Molecular and morphological research conducted over the past 17 years by Senior Principal Research Scientist Dr Peter Weston and his colleagues, on the phylogeny of the Proteaceae has been coming to fruition in recent years, providing a new framework for testing how geological, climatic and evolutionary processes have shaped the family. A new interpretation of the evolution of sclerophyllous leaf anatomy in the family, published in 2005, a new classification of the family, (2006), and the first molecular dating analysis of the family, (2007), are the results of this work. Progress towards the completion of these studies continued in 2007-2008 with the publication of an analysis of the functional significance of sunken and encrypted stomata as adaptations that minimize water loss through transpiration in the Proteaceae (Jordan et al. 2008).

This study corroborated the long-standing idea that stomata that are deeply buried in crypts and grooves on the leaf surfaces of various species of Persoonia, Franklandia, Lambertia, Banksia, Hakea and Grevillea did indeed evolve as adaptations to reduce water loss. Stomata that are shallowly buried in papillose pits have also been postulated as adaptations minimising water loss, but the multiple evolutionary origins of these structures were shown to be uncorrelated with dry environments. Other explanations for the evolution of these structures need to be sought and tested. Ever since continental drift and plate tectonics displaced the stable earth model in geological theory, the Proteaceae have been generally regarded as a classic ‘Gondwanic Group’ - one that originated well before the fragmentation of the ancient supercontinent Gondwana, and which achieved its widespread distribution in the southern hemisphere as a result of vicariance. However, molecular dating analyses recently conducted by Dr Weston’s research group are suggesting that the first of these ideas is false and the second only partly true. Mast et al. (2008) published the results of a phylogenetic analysis and molecular dating of the most biogeographically interesting clade in the Proteaceae, the tribe Macadamieae, based on DNA sequence data for seven nuclear and chloroplast genes plus morphology. Their results strongly suggest that at least 8 of the 9 clades in this tribe showing intercontinental disjunctions are too young to have dispersed between the continents over land. It suggests instead that what is now the Australian craton is the centre of origin of this tribe and that the clades now found in tropical and temperate South America, New Caledonia, Fiji, Vanuatu, South East Asia, Madagascar, and southern Africa got there by long distance dispersal across significant ocean gaps. Moreover, the reconstructed dispersal events all post-date the onset of the circum-polar current and are significantly correlated with multiple evolutionary origins of indehiscent fruits, suggesting that the intact fruit wall has played a key role in protecting the seed from immersion in sea water.

Did you know?

  • Proteaceae includes waratahs (genus Telopea), Grevillea, Macadamia, Banksia, Protea and 75  other genera.
  • Most of the species are found in Australia and southern Africa but the family extends throughout most of the southern hemisphere and into SE Asia.
  • Fossil pollen of the South American waratah, 55 million years old, has been found in SE Australia.
  • Species in the Proteaceae are pollinated by nectar-feeding birds, bees, butterflies, moths and even  tiny possums.
  • Edible nuts are harvested from Macadamia.
  • Telopea is a valuable cut-flower export.
  • Protea, grown in many Sydney gardens is native  to southern Africa.

DNA of Proteaceae

The family Proteaceae - containing iconic plants like waratahs, banksias, grevilleas and hakeas - is represented on all of the continental landmasses of the Southern Hemisphere, with some extensions into the Northern Hemisphere and the Pacific Islands. This distribution reflects an origin for the family on the ancient southern ‘supercontinent’ of Gondwana, at least 100 million years ago. According to this theory, the ancestors of the great majority of living species of Proteaceae ‘drifted’ with the continents after the fragmentation of Gondwana.

Scientists at the Royal Botanic Gardens & Domain Trust are testing this idea by reconstructing the evolutionary history of the Proteaceae using information from DNA sequences. Geologists are confident of their knowledge of the splitting sequence of Gondwanic continents over the last 130 million years. This allows us to make predictions concerning expected evolutionary relationships between the Proteaceae of different Gondwanic fragments. For example, we expect the Proteaceae of New Caledonia and Australia to be more closely related to each other than they are to African Proteaceae because the African continent rifted from the rest of Gondwana earlier than either Australia or New Caledonia.

The family Proteaceae is absent from very few regions of Australia. Anyone who has spent time in the Australian bush or even wandered around parks and streets in just about any Australian town would be familiar with some members of the family. They are also becoming increasingly familiar on supermarket shelves, as food (macadamia nuts) or as cut flowers or potted plants (waratahs, banksias, proteas, leucadendrons and leucospermums).

The Nightcap Oak Eidothea hardeniana

A new species of rainforest tree dating back to prehistoric Gondwana has been identified in the Nightcap Range, near Lismore on the State’s North Coast.

Sixteen trees of the newly named Eidothea hardeniana are in an isolated part of the Range, leading to comparisons between this discovery and the ancient Wollemi Pine found in 1994. The exact location of these trees is being kept secret as they may be vulnerable to disease carried by people and could be prized by poachers and seed collectors.

Ecologist Robert Kooyman who discovered the species, sent leaves, fruits and wood from the tree to Peter Weston, our Proteaceae specialist, who identified the plants as belonging to the Eidothea genus. Peter Weston & Robert Kooyman have named the species Eidothea hardeniana in honour of Gwen Harden, a former botanist at the Royal Botanic Gardens and editor of the Flora of New South Wales, ‘whose career has been devoted to improving our knowledge of the flora of New South Wales, particularly of the State’s rainforest plants.

Environment Minister Bob Debus praised Robert Kooyman and Dr Peter Weston for their work. ‘National Parks and native forests are vital biodiversity storehouses and although we know a lot about them they have many more secrets yet to be revealed. This discovery clearly demonstrates the importance of protecting our native forests. Many of these fascinating trees are thankfully within the World Heritage Listed Central Eastern Rainforest Reserve.

‘The Nightcap Range is the cradle of rainforest conservation in NSW and this find would not have been possible if the community and government had not acted to protect these beautiful places. The importance of these magnificent forests is continuing to be proved by discoveries such as this.’

An interesting thing about these trees is that they have eluded scientific classification for so long. In the 1950s leaves of the Nightcap species were found but not identified as a new species.

Eidothea hardeniana are ‘living fossils’ of the rainforests which once covered the ancient supercontinent of Gondwana, consisting of what are now Australia, Africa, South America, Antarctica and New Zealand. But while some existing Australian rainforest trees come from lineages which diversified into hundreds of species, Eidothea remained almost unchanged.

The Botanic Gardens Trust and the National Parks and Wildlife Service are supporting the listing of this new species as an endangered species so that it is protected by the Threatened Species Conservation Act.

 

Leucodendron leaf section
Transverse section of a
Leucadendron pubescens leaf showing a papillose pit. Scale bars = 50 μm.

Banksia leaf section
External, abaxial surface of a Banksia quercifolia leaf showing the hair-filled apertures of two stomatal pits.

Peter-Weston

waratah

009311.jpg

Alloxylon

Embothrium

Nightcap Oak