Eucalyptus aggregata black gum
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.
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.
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).
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, SP). Mention of flower fragrance and West Texas removed; minor edits (Jun 2023, SP).