Eucalyptus obliqua - Messmate Stringybark, Messmate, Stringybark, Brown-top, Brown-top Stringybark,  Australian Oak, Tasmanian Oak (Southeast Australia) This is the euc first analyzed by anyone from the Western world on Captain Cook's third voyage, and the species from which the entire genus derives its name.  It is a very large tree, capable of reaching heights up to 150' in a favorable situation (much taller in the wild in moist forests).  One of the "strinybarked ashes", with affinities to E. regnans and E. delegatensis as well as the stringybarks.  Prefers a cool moist site, but also tolerates some dryness and poor soils.  Exceptionally attractive in a cool, moist situation; where on older trees the foliage is held in meandering upright clusters which contrast excellently with the grey fibrous bark.  Seems to have a bit more shade tolerance than the average euc.  This tree's widespread distribution has resulted in a wide variety of provenances; most in cultivation are not of hardy provenance.  4 to 17°F.
Photos of Eucalyptus obliqua

Eucalyptus obtusiflora - Port Jackson Mallee, Dongara Mallee (Australia) A fairly hardy mallee of moderate growth.  Hardiness somewhere in the vicinity of 8 to 15°F.

Eucalyptus olsenii - Woila Gum (New South Wales) A rare species of restricted natural distribution; has smooth bark and short green ash-like leaves.  Juvenile plants have fantastic leaves with stiff little hairs, and subsequent leaves have striking reddish new growth.  It requires good drainage and is difficult to grow in clay soils.  The seed is surprisingly large.  Cold tender when young, but capable of withstanding about 6°F at maturity.
Photos of Eucalyptus olsenii

Eucalyptus oreades - Blue Mountains Ash, Smooth-barked Mountain Ash, White Ash (New South Wales, Queensland) A tall, dense-crowned species with attractive peeling white bark and shiny green leaves.  Adaptable.  9 to 16°F.

Eucalyptus ovata - Swamp Gum, Large-flowered Swamp Gum, Marrawah Gum, Black Gum, Blue-leaved Sally (southeast Australia) Probably one of the best known swamp gums for its heat tolerance and ease of growth.  Characterized by smooth grey bark and a rather dark, low crown of green leaves held in tufts at the ends of the branches.  Inferior to E. gunnii for infertile swampy soils.  Slightly overrated for hardiness by some nurseries.  6 to 14°F.

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