Corymbia citriodora (syn. Eucalyptus citriodora)
lemon-scented gum

Myrtaceae (myrtle family)
Queensland
Corymbia citriodora, Math Court. John Rawlings, c. 2006

A strikingly handsome tree with a slender trunk and thin white bark, soaring more than half its total height to the lowest branches. The white flowers occur in panicles rather than cymes, but are generally too high to see (unlike the panicles of E. polyanthemos). Gum tree leaves vary a lot in smell when you crush and sniff them because the mix of oils varies from one species to the next, but with the lemon-scented gum the oil is virtually pure citronellal, known as a germicide and mosquito repellent, but with a marvelous aroma for humans. In colder sites on campus, trees well over 30 feet have succumbed to our occasional freezes.

Between the Durand and McCullough buildings there are three tall trees. A handsome pair in the outer northwest Quad show how a tall trunk with no branches at all up to a substantial height leaves a detectable record of bygone branches in the form of dimples and pimples on the otherwise smooth trunk. As a branch becomes shaded from sunlight as a result of growth in height, abscissic acid (a plant hormone) causes a brittle zone to form at the trunk. Wind then breaks the branch off cleanly. Higher up on these two trees are branchlets that were killed by freezing; no living tissue remained to respond to the hormone. Consequently, these sticks will remain visible for years. Research on abscissic acid has received military support aimed at defoliating forests.

More recent plantings have been attempted on Serra Street at the Schwab Residential Center. Occasional juvenile leaves can be found near ground level that have a visibly rough undersurface made up of tiny projections containing lemon oil. After you feel the sandpaper-like texture, smell your fingers! Onlookers are astonished by the fragrance; you can put these leaves in your gin and tonic!

About this Entry: The main text of this entry is from the book Trees of Stanford and Environs, by Ronald Bracewell, published 2005.