Botanic Gardens Trust, Sydney, Australia

Poales

Phylogeny of the restiid clade of Poales

Barbara Briggs Honorary Research Associate, and Adam Marchant 
 
The plant families of the restiid clade are close relatives of the grasses, within the economically important major plant group Poales. Three families, Restionaceae, Anarthriaceae and Centrolepidaceae have generally been recognised. An evolutionary tree or phylogeny of this group and in particular the Australian species of Restionaceae has been produced, based on DNA data from the chloroplast genome.

Now that affinities are better known, it is clear that some of the Australian 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 will involve enlarging the genera Leptocarpus and Desmocladus by combining several genera.

The phylogeny also indicates that the Centrolepidaceae, which has long been recognised as a distinct family, is embedded in Restionaceae and best treated as a subfamily of Restionaceae. In appearance the miniscule centrolepid plants differ greatly from the much larger restiads, and their flowers show remarkable differences from floral types found in other members of the Poales. Restionaceae mostly have separate male and female plants but centrolepid flowers are bisexual. A paper presenting these findings has been submitted to the international botanical journal ‘Taxon’.

The Restionaceae of South Africa are only distantly related to the Australian genera and are classified in a different subfamily. An opportunity to see a variety of African species gave interesting comparisons of their morphology and habitats.

BB-Staberoha-banksii-female
Staberoha banksii,
a South African species of Restionaceae with very different male and female inflorescences (female inflorescence)

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Staberoha banksii - Male inflorescence

Photos: Barbara Briggs