Eucalyptus aggregata black gum

Eucalyptus aggregata trunk, Stanford Avenue. Sairus Patel, 10 Jun 2023

Eucalyptus aggregata buds, fruit, and leaves; Stanford Avenue. Sairus Patel, 10 Jun 2023

This is a tree from places with cold winters. The leaves are on the narrow side, up to ½ inch wide, and up to 3 inches long. The fruits come in groups of seven, each up to ⅕ inch in diameter. The flowers are small and undistinguished. The bark is hard and fibrous, a rich orange-brown but not black. There is a 40-foot specimen, 25 inches in diameter, in the Stanford Avenue greenbelt behind 836 Santa Fe Avenue, planted in 1973.

Eucalyptus aggregata, trunk on the right, overhangs the path at Stanford Avenue. Sairus Patel, 10 Jun 2023

Eucalyptus aggregata voucher. Courtesy of Prof. Matt Ritter and Robert F. Hoover Herbarium, Cal Poly State University

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), otherwise-hardy trees will be killed.

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

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.