Eucalyptus macarthurii - Camden Woollybutt, Paddy's River Box (Southeast Australia) Fast-growing, heavy-set, dark-looking tree with a dense symmetrical canopy.  Leaves are often used for oil distillation.  Adaptable and useful on heavy soils.  Has potential throughout the South and Southwest.  Achieves great hardiness with age.  5 to 15°F.
Photos of Eucalytpus macarthurii

Eucalyptus macrocarpa - Rose-of-the-West, Blue Bush, Desert Mallee, Mallee Rose, Mottlecah, Small-leaved Mottlecah (Western Australia) A low, rambling species with thick, rounded leaves and large bright red flowers in clusters on the stems.  Tolerates considerable cold in desert climates but is succeptible to fungal problems and grows slowly in maritime climates - a hot, sunny, sheltered position with excellent drainage may aid its survival.  10 to 25°F.

Eucalyptus macrorhyncha - Red Stringybark, Cannon's Stringybark, Capertee Stringybark (Southeast Australia) A medium stringybark with attractive deeply fissured, red and grey bark.  Somewhat drought tolerant.  Not frequently grown, but possibly hardy to around 8 to 16°F.
Photos of Eucalyptus macrorynchna

Eucalyptus malacoxylon - Moonbi Apple Box (Australia) related to E. bridgesiana.

Eucalyptus mannifera - Brittle Gum,  White Brittle Gum, Broad-leaved Manna Gum, Capertee Brittle Gum, Manna Gum, Mountain Spotted Gum (Southeast Australia) This is a group that deserves more attention, because they are very beautiful ornamentals and more cold-hardy than is realized.  They have attractive green-grey leaves (though more bluish in cooler climates) and outstanding powdery bark in pastel shades of light pink, cream and white.  Australian Aborigines have used the white powder to paint their faces.  Several subspecies exist, and are now listed by some references as their own species.  All are tolerant of heat and cold and should be tried in the South US.  4 to 12°F (?)

• Ssp. elliptica - Brittle Gum has round, stem-clasping juvenile leaves, white powdery bark, and soft pinkish new growth; and is probably the most common in cultivation.  It is often classified as its own species, E. elliptica.
• Ssp. gulickii grows at higher elevations and may contain the hardiest provenances of this group.
• Ssp. maculosa has bark that develops reddish patches and is shed in small flakes.
• Ssp. mannifera has "willow-like" juvenile leaves resembling those of E. nicholii.
• Ssp. praecox has a mottled trunk and inhabits very rocky areas in habitat.

Eucalyptus melliodora - Honey Box, Yellow Box, Yellow Ironbark, Yellow Iron Box (southeast Australia) A medium tree, a favorite food of the koala, and one of the best eucs for honey production.  Probably not hardy beyond 15°F, contrary to some references: it often does not perform well even in mild winters in the Pacific Northwest.
Photos of Eucalyptus melliodora

Eucalyptus michaeliana - Hillgrove Gum, Brittle Gum (New South Wales) A rare, fast-growing, attractive species, not thoroughly tested for cold-hardiness in cultivation.  Possibly hardy to 8 to 15°F.

Eucalyptus microtheca - Coolibah (Coolabah), Flooded Box, Western Coolibah (Australia, exclding Victoria and Tasmania)  This species is exceptional in that it grows throughout a very large area of Australia, particularly in arid and semi-arid regions.  In these areas it prefers to inhabit seasonally flooded streambanks and riverbeds.  It has rough bark and a broad, spreading habit.  It has been grown in the Southwestern United States for some time, including arid regions that can get quite cold, and is certainly worth trying in cooler maritime climates as well.  It also seems better able to tolerate drastic changes in temperature than many species, and therefore grows reasonably well in parts of the Southern United States.  Unlike most other species, it can often be a challenge to train it upright and sometimes a short stake must be used.  Because of its large natural range, the hardiness of this species is likely to be extremely variable.  It should be tried in USDA zone 9 in such places as the Pacific Northwest and Britain, and in colder zones in places that have hotter summers or drier winters.  7 to 20°F.
Photos of Eucalyptus microtheca

Eucalyptus mitchelliana - Mount Buffalo Gum, Mt Buffalo Sallee (Mount Buffalo Plateau, Victoria) A very attractive small to medium tree, closely related to E. stellulata.  Has very smooth, often colored bark, and an open crown of small pendulous leaves.  Exposure tolerant.  Rare in the wild, but has been in cultivation for some time - there are old specimens to be found in the British Isles.  It is often a bit slow to establish, and shows a definite preference for cool-summer climates and sharp-draining, rocky soils reminiscent of the screes it inhabits natively.  2 to 8°F.
Photos of Eucalyptus mitchelliana

Eucalyptus moorei - Narrow-leaved Sallee, Little Sallee (New South Wales) A rather small, slow-growing eucalypt, which often inhabits high craggy places.  May eventually reach about 30' high; tolerates poor drainage.  It is related to E. mitchelliana and E. stellulata.  Approximately 2 to 10°F.

• Var. nana is even smaller.

Eucalyptus morrisbyi - Morrisby's Gum (Tasmania) A low elevation species, rare in the wild; very attractive and surprisingly hardy for a low elevation tree.  It is closely related to E. gunnii and E. urnigera, but takes on a more picturesque and exotic looking habit with age, and has smooth bark that is more attractive than that of most E. gunnii.  4 to 12°F.
Photos of Eucalyptus morrisbyi