Botanic Gardens Trust, Sydney, Australia

Poales

Aligning classification with phylogeny in the restiid clade of Poales

Barbara Briggs - Honorary Research Associate, Adam Marchant - Molecular Systematics Officer, Andrew Perkins

In studies of Australian species of plant family Restionaceae, and the related Anarthriaceae and Centrolepidaceae, an extensive program of sequencing chloroplast DNA has been completed. The data have been analysed to develop hypotheses of relationships. These are close relatives of the grasses and constitute the restiid lineage within the economically important major plant group, Poales. 

Now that affinities are better known, it is clear that some of the genera currently recognised are polyphyletic, encompassing several species that are not closely related, or are paraphyletic, since other groups are embedded within them. As a result, changes are needed to produce a classification that accords with the evolutionary relationships but in which the genera may also be recognised by their morphological features. This involves enlarging Leptocarpus and Lepidobolus by combining several genera, so that fewer genera than in the present classification will be recognised.

The molecular data also give evidence that the Centrolepidaceae, which has long been recognised as a family, is embedded in Restionaceae and should instead be treated as a subfamily of Restionaceae. In appearance the miniscule centrolepid plants differ greatly from the much larger restiads, but they show resemblances to the seedling stages of restiad plants. Papers are being prepared to present the new data and conclusions, and to make the necessary changes in classification and nomenclature.

Descriptions have also been drawn up for nine new species, which have not previously been botanically named. They will be named in the genera that will be recognised when the classification is better aligned with the phylogeny, as a result of this study.

Assembling the monocot tree of life

Barbara Briggs and Gwen Harden - Honorary Research Associates
 
Monocotyledons are a major group of flowering plants, including grasses, palms, sedges, lilies, orchids and much more. Within monocots, the most important as food sources for humans are the grasses: the source of wheat, corn, rice, cane sugar and fodder for animals. Grasses comprise the family Poaceae and, together with related plant families, such as Restionaceae and Cyperaceae, they make up the Order Poales.

For several years Barbara has been part of an international collaboration to determine evolutionary relationships within the monocots worldwide. This has involved researchers in many centres in the USA, Canada and Australia. They have based their findings on analyses of data from the whole of the chloroplast genome. Most of the DNA extraction and sequencing was done in the USA, but this required the collection and sending of representative species from many countries. Some of the collections sent for study were from joint fieldwork in north-eastern NSW with Honorary Research Associate Gwen Harden. Alex Floyd of the North Coast Regional Botanic Garden at Coffs Harbour also assisted with the fieldwork.

The first major paper from this collaboration has now been published in the Annals of the Missouri Botanical Garden. This reported on analyses of 81 chloroplast genes in 83 species, representing the families of Poales and its relatives. This gives a clearer picture than previously possible of the relationships of the families, including determining the closest relatives of the grasses. It also shows that there have been five separate events in the evolution of Poales when lineages have shifted from insect pollination to wind pollination, with associated changes in the structure of the flowers. These evolutionary changes also appear to be correlated with changes in the predominant habitats. Studies of relationships of other monocot groups are continuing.

Centrolepis-polygyna---B-Briggs-2012
Centrolepis polygyna. Photo: David Hardin

Barbara Briggs & Gwen Harden
Honorary Research Associates Barbara Briggs and Gwen Harden collecting rainforest plants for the Monocot project. Photo: Alex Floyd

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