Eucalyptus camaldulensis
river red gum

Myrtaceae (myrtle family)
Eucalyptus camaldulensis flower buds. John Rawlings

River red gum, one of the eucalypts most commonly seen in California, grows along rivers over most of Australia, from the wet tropics to cool temperate regions, withstands arid conditions, and if flooded for long periods does not succumb. It has two root systems: one for surface moisture, if any, and deep penetrating roots for subsurface water. In tests in overseas climates with low rainfall it outperformed Tasmanian blue gum for wood production and is now seen all around the Mediterranean; in several countries it is the only eucalypt used.

The wood is hard, dense, and red – hence the common name. The Latin name, given in 1832 by Frederick Dehnhardt (1787–1876), refers ultimately to a congregation of monk hermits founded a thousand years ago in Tuscany at Camàldoli. At the time, Dehnhardt was head gardener to the Count of Camàlduli in Naples.

Red gums were planted as an avenue on Searsville Road and in scattered locations. Other old specimens can be seen across Galvez Street from the football stadium. Meanwhile, river red gum continues to be a popular choice for new planting on dry sites, for example on the west side of Campus Drive East between Serra Street and Escondido Road, where it has been under serious attack by the lerp insect, a species of psyllid.

Eucalyptus camaldulensis buds and fruit capsules. From Australia Forestry and Timber Bureau, Illustrations of the buds and fruits of eucalyptus species, 4th ed., 1962

Buds in sevens, with conical opercula, can always be found, though sometimes there are as many as 11. In case of doubt, look for juvenile leaves; while not so very different in shape from the mature leaves (a little shorter and broader), the juvenile leaves are distinctly bluish and identify campus red gums at a glance. The papery opercula, pushed off by the growing flowers, fall on the ground, sometimes with the sound of light rain. The benign litter soon blows away. If you are observant and catch the flower buds as they are developing you can find a tiny second operculum.

Just as the operculum represents the fused petals of an ancestral plant, so the outer operculum represents the bracts that surrounded those petals. When the eucalypts long ago dispensed with petals as an attractant to pollinators, economically relying on the sex organs alone for color, the operculum was assigned the role of covering the delicate growing stamens. Hence the name eucalyptus, meaning well covered. The name of the nymph Calypso (unconfirmed daughter of Atlas), who troubled Odysseus, has the same Greek origin.

Operculum in Latin means lid, the same word that is used for the hard trapdoors that protect small marine molluscs and are found on beaches as white discs with spiral engraving.

Related material: Eucalyptus checklist.

About this Entry: The main text of this entry is from the book Trees of Stanford and Environs, by Ronald Bracewell, published 2005. John Rawlings subsequently changed the number of buds that can be sometimes found in a cluster from 10 to 11.