Annals of Botany 89: 605-612, 2002
© 2002 Annals of Botany Company
The Anatomy and Chemistry of the Colour Bands of Grasstree Stems (Xanthorrhoea preissii) used for Plant Age and Fire History Determination
0School of Chemical and Biological Sciences, Curtin University of Technology, PO Box U1987, Perth WA 6845, Australia
* For correspondence. Fax 0061 8 9266 2495, e-mail rlamontb{at}cc.curtin.edu.au
Received: 5 September 2001; Returned for revision: 30 November 2001; Accepted: 7 January 2002.
A new method of ageing and determining the fire history of grasstrees, based on colour bands running along the stem, has been developed. As part of our evaluation of the technique, we examined the structural and chemical basis of the colour differences. Exposed ends of the leaf bases are cream, brown and black, with the inner cortex, especially in the black leaf bases, being darker than the outer cortex. There was no structural difference between the three leaf base types. Tannin concentration increased from cream to brown to black leaf bases, and from the inner to outer cortex, and remained quite stable over many years. Both water-soluble and insoluble pigments contribute to the darkness of the black leaf bases. A hydrophobic naphthoquinone was present in the conducting tissues of the vascular bundles, and related naphthalene-derivatives were present in the surrounding tissues. We conclude that the colour differences between the leaf bases have a chemical basis that can be linked to environmental changes: tannin cells to phenological effects, and naphthalene-derivatives in the vascular core to the passage of fire.
Key words: Age determination, fire history, grasstrees, growth rings, leaf anatomy, leaf bases, monocotyledon, naphthoquinone, resin, tannin, vascular bundles, Xanthorrhoea.