Floral structure and development in the dioecious Australian endemic Lomandra longifolia (Lomandraceae)
Nabil M. Ahmad A , Peter M. Martin A B and John M. Vella AA Amenity Horticulture Unit, University of Sydney Plant Breeding Institute, PMB 11, Camden, NSW 2570, Australia.
B Corresponding author. Email: pmartin@camden.usyd.edu.au
Australian Journal of Botany 56(8) 666-683 https://doi.org/10.1071/BT07223
Submitted: 17 December 2007 Accepted: 30 October 2008 Published: 15 December 2008
Abstract
The micromorphology and histology of the development of male and female flowers of the dioecious Australian endemic species Lomandra longifolia Labill. was studied by means of scanning electron microscopy and light microscopy of entire and sectioned material. Although mature flowers are functionally unisexual, in the early stages of development pistillate and staminate flowers are identical and apparently bisexual. In a sequential fashion, six perianth parts are initiated within two alternating whorls, the sepals first and the petals second; six stamens are initiated in two alternating whorls of three stamens each, the first opposite the sepals and the second opposite the petals; and last, a central gynoecium is initiated. Following initiation, the two flower types diverge developmentally when the stamens become bilobed. In male flowers, cytological analysis of the slowly growing abortive pistil shows that megasporogenesis does not occur. Pistil abortion happens before meiosis whereas the stamens continue to develop until maturity and dehiscence. In female flowers, stamen arrest occurs before the onset of meiosis in microspore mother cells, after which the pistil continues its development through megasporogenesis and megagametogenesis. In all, 14 stages of floral development of both male and female flowers have been designated. Stages 1–6 of the two flower types were common to both sexes.
Acknowledgements
We warmly thank all staff of the Electron Microscopy Unit, University of Sydney, and particularly Dr Ian Kaplin and Mr Tony Romeo for their very able help in using the SEM. We also express our deep gratitude to Dr Jane Radford, the manager of the Histopathology Laboratory, University of Sydney, for permission to work in her laboratory and for her help on numerous practical aspects. Thanks are also due to Professor R. A. McIntosh for assistance in the preparation of the manuscript. Finally, we thank Leppington Speedy® Seedlings Pty Ltd for the provision of plant material and financial support.
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