Eucalyptus aggregata
black gum

Myrtaceae (myrtle family)
New South Wales, Victoria
Eucalyptus aggregata voucher. Courtesy of Prof. Matt Ritter and Robert F. Hoover Herbarium, Cal Poly State University

This is a tree from places with cold winters and a candidate for paper production in West Texas, where any tree is difficult to grow and whose main virtue is that land is cheap. The leaves are on the narrow side, up to ½ inch wide, and up to 2½ inches long. The fruits come in groups of four to eight each, not much more than ⅛ inch in diameter. The flowers are small and undistinguished except for being fragrant, uncommon in a eucalypt. To encounter the pleasant aroma at ground level can be puzzling because the flowers are too high to be seen and one is more likely to look for a nearby shrub as the source. However, there will be tiny fallen opercula in the ground litter to verify the source. The bark is hard and fibrous, dark orange but not black.

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

There is a 40-foot specimen, 25 inches in diameter, in the Stanford Avenue greenbelt behind 836 Santa Fe Avenue, planted in 1973.

Black gum is known to withstand temperatures of 12° F. Such trees were not preferred among those that were chosen for experimental plantings in the Bay Area, for obvious reasons. But cold resistance does not disqualify a tree as an ornamental; in fact, several of our commoner campus eucalypts are not bothered by temperatures below zero. Temperature alone is not an adequate indicator of cold resistance. If the temperature drops below 32° F and stays there day and night for three days, as happened in 1972, many plants will die. Also, if the temperature drops from 50° F to below zero in a few hours (which thankfully does not happen here but does in West Texas), otherwise-hardy trees will be killed.

Name derivation: Eucalyptus – from the Greek eu, good or well, and kalyptos, covered, referring to the calyx which forms a lid over the flowers when in bud; aggregata – flocking together, or growing in groups, clustered (from California Plant Names).

Related material: Eucalyptus checklist | Eucalypt voucher gallery.

About this Entry: The main text of this entry is from the book Trees of Stanford and Environs, by Ronald Bracewell, published 2005. Location verified Jul 2020 by Sairus Patel.