Botanic Gardens Trust, Sydney, Australia

Myrtaceae - Biology

Dr Peter Wilson - Senior Research Scientist

Dr Peter Wilson and Dr Maurizio Rossetto received a small grant from the Australian Flora Foundation to work on the reproductive biology and population genetics of the Magenta Lilly Pilly (Syzygium paniculatum). This species is listed as vulnerable under both New South Wales (TSC Act) and Federal (EPBC Act) legislation and is found only in NSW where it has a restricted distribution: it occurs in geographically disjunct areas along a relatively narrow coastal strip from just south of Forster to not far south of Nowra.

The reproductive biology of this species is different from all other Australian species of Syzygium in that its seeds are frequently polyembryonic. Polyembryony is a feature that has been shown, in a few Asian species of the genus, to be the result of a form of apomixis where adventitious embryos arise from nucellar tissues in the ovule. Although fertilisation of the ovule does occur and results in endosperm formation, which is necessary for embryo development, it is not certain how many of the seeds contain zygotic embryos. Apomixis could reduce genetic diversity within each population and perhaps increase genetic divergence between populations; it could thus be a major factor in the species’ rarity and have implications for its conservation and for the development of a Recovery Plan.

An honours student, Ms Katie Shields, has begun work on this project and will be using population genetics techniques to examine genetic diversity in populations and in seedlings. There are three main aims to this study. One aim is to determine the genetic diversity within and between populations of the species; this will involve taking leaf samples from plants in as many sites as possible to assess genetic diversity across the entire species and within populations. The second aim is to test whether any of the embryos are the result of fertilisation or whether all are genetically identical to the parent plant; this will be done by parentage analysis using genetic markers. The third aim is to monitor and analyse the multiple seedlings that can arise from a single seed to determine whether the ‘fittest’ seedling is the one resulting from the fertilised ovule.

DNA studies of the Myrtaceae

My research work with the Royal Botanic Gardens & Domain Trust has led to the rearrangement of the groups within the Myrtaceae (or Myrtle) family. This is a large plant family that includes the Australian bottlebrushes and eucalypts (gum trees). Plants in the Myrtaceae can usually be recognised by their showy stamens and aromatic leaves. Using new information from DNA, I discovered that the plants called Tea-trees are not all related to each other, showing that appearances can be deceiving. Getting relationships right can help predict disease susceptibility and assist in horticultural development.

Did you know?

  • The Myrtaceae includes Eucalyptus, Leptospermum, Melaleuca, Callistemon and many other genera.
  • The tallest hardwood tree ever measured was an Australian Mountain Ash, Eucalyptus regnans.
  • Eucalypt woodchips provide pulp for fine writing and printing paper. Over 55% of woodchips come from native forests.
  • European Myrtle was grown in ancient Rome and clipped regularly to release the scent of its fragrant oils
  • Foods from the Myrtaceae include guavas, allspice and cloves.
  • The Crepe Myrtle is not in the Myrtaceae but does belong in a closely related family.

Syzygium germinating
Germinating seed showing multiple shoots Photo: Katie Shields

Leptospermum spectabile