Botanic Gardens Trust, Sydney, Australia


Resolving nodes on the Tree of Life: tiny plants with a big story

Barbara Briggs, Honorary Research Associate, National Herbarium of NSW

Gene sequences and analyses of genetic data have made it possible to build the ‘tree of life’, a ‘family tree’ that shows evolutionary relationships of organisms. This has made recent decades a most exciting time in biological science. Our Herbarium and DNA laboratory are contributing to this with studies of the Restionaceae and their relatives, as well as research on many other plant groups.

Restionaceae, the restiads, are a southern-hemisphere family related to the grasses, with species mainly in Australia and South Africa. Some occur in arid areas but most are in swamps or winter-wet sites. Our studies revealed many new species and nine have recently been named in our scientific journal Telopea.

Plants thought to be related to Restionaceae were included in the study and gave varied and unexpected results. A group of tiny aquatic plants, Hydatellaceae, was found to be not at all closely related to the restiads, instead they are primitive flowering plants related to water lilies! Their structures are so small and modified that they had been badly misclassified. In that work we cooperated with botanists from Canada and Britain.

Another group, the centrolepid plants, are also among Australia’s smallest flowering plants. Seven species of Centrolepis occur in moist sites in NSW and about 30 are native to other parts of Australia. Other genera, Aphelia and Gaimardia, are in other Australian states. Their flowers are very unusual, but studies by botanists in England and Russia have found that what was thought to be a cluster of flowers is actually a single flower.

Research published recently with colleagues Adam Marchant and Andrew Perkins, shows that they not just relatives of the restiads, but should be classified as part of that family. DNA indicates that they evolved from the Australian branch of the restiads, and they flower and fruit at a stage equivalent to seedlings of the much larger restiad plants that resemble their ancestors. This finding resolves another node of the family tree of the flowering plants, now that we better understand how these plants are related.

Why were these plants wrongly classified before this work was done? Their structures are highly modified and difficult to interpret until DNA gave new insights into their relationships. Botanical knowledge is fast increasing but there is still much to discover.







Leptocarpus scariosus
Leptocarpus scariosus, a restiad, in a winter-wet summer-dry swamp in Western Australia

Trithuria filamentosa, Hydatellaceae, collected in Tasmania 

Aphelia brizula, a Western Australian centrolepid. Photo Andrew Perkins