Eucalyptus cadens - Wangaratta Gum (Victoria) Extremely rare.  Related to E. aggregata and E. rodwayi but has glaucous new growth.  Possibly hardy to 0 to 5°F or thereabouts.

Eucalyptus caliginosa - Broad-leaved Stringybark, New England Stringybark (New England Plateau, New South Wales and Queensland) A rather slow-growing stringybark that takes a while to acquire full hardiness.  5 to 14°F.
Photos of Eucalyptus calignosa

Eucalyptus camaldulensis - River Red Gum, Murray Red Gum, Red Gum, River Gum, Yarrow (Australia) This tree is remarkable in that it grows along rivers throughout the entire Australian continent while most species have a rather limited natural range.  It has attractive light green foliage and grows fast to 100' where hardy, often with a curved trunk. Beyond that its characteristics are quite variable, and so is its hardiness, due to such a large natural range.  Var. obtusa may contain the hardiest provenances.  Good in greenhouse or as an annual foliage plant (though it may establish itself as a perennial and grow back every spring); perhaps good as a patio plant also if brought indoors during cold periods.  It may not produce its characteristic fast growth in cool summer climates, unless all other conditions are ideal.  This tree is often seen naturalized in California's Central Valley and in many other parts of the world.  10 to 22°F.
Photos of Eucalyptus camaldulensis

Eucalyptus camphora - Mountain Swamp Gum, Broad-leaved Sally, Swamp Gum (southeast Australia) This tree is esteemed for its ability to do well in poor clay soils and withstand prolonged waterlogging.  It has short broad reddish leaves, greyish-brown smooth peeling bark, and can grow to about 80' tall.  It also tolerates dry conditions and is very fast-growing with bright, deep green leaves.  Several subspecies exist, and most plants in so far cultivation seem to be of cold-tender provenance.  3 to 14°F.
Photos of Eucalyptus camphora

Eucalyptus cephalocarpa - Silver-leaved Stringybark, Silver Stringybark, Mealy Stringybark A fast growing, hardy, and attractive tree, seldom cultivated.  Allied to E. cinerea.  8 to 14°F.

Eucalyptus chapmaniana - Bogong Gum (Mount Bogong and Mount Baw Baw area, Victoria) Although rare and inconspicuous in the wild, this species has great potential in cultivation.  It tends to develop a short trunk and very long branches, vaguely resembling the tropical-looking, cold-tender eucs of northern and western Australia.  It has very large leaves tapering to a point, and (in the wild, at least) a rough barked trunk with smooth white or grey limbs.  E. chapmaniana is closely related to E. rubida, and may tolerate slightly poor drainage.  Seldom cultivated, but likely to be hardy to 4 to 10°F.
Photos of Eucalyptus chapmaniana

Eucalyptus cinerea - Siver Dollar Eucalyptus, Argyle Apple, Mealy Stringybark (Australia) A moderate to fast growing, completely silvery tree with a low thick irregular crown.  This is the most common species sold as a foliage plant for bedding in the United States.  Tolerates heat well in the Southeast US within the range of its hardiness.  8 to 16°F.  Ssp. triplex from ACT is larger and may be considerably hardier but is probably not known in cultivation.
Photos of Eucalyptus cinerea

Eucalyptus coccifera - Mount Wellington Peppermint, Tasmanian Snow Gum (Tasmania) From freezing alpine regions, this tree prefers cool summers and usually grows to about 80' in cultivation, shorter in exposed or hot areas.  Somewhat slow to establish, but grows faster with age.  The juvenile leaves are usually green and often purple underneath, produced on warty orangeish-yellow stems, and variable in shape; the mature ones longer and bluish on smooth stems.  Often classified as one of the "Snow Gums", although it is genetically more akin to the peppermints.  Long renowned for cold-hardiness in Britain; hardiest trees may come from provenances established there.  0 to 14°F.
Photos of Eucalyptus coccifera

Eucalyptus conica - Fuzzy Box, Fuzzy Gum (New South Wales) Probably hardy to 8 to 16°F.

Eucalyptus consideniana - Yertchuk, Prickly Stringybark, Pricklybark (Australia) A fast, tall-growing tree having long large leaves with a rather yellowish-orange tint and very rough brown-grey bark.  Tolerates poor drainage.  12 to 17°F.
Photos of Eucalyptus consideniana

Eucalyptus conspicua - Silver-leafed Stringybark (Australia) Similar to E. cinerea.

Eucalyptus cordata - Heart-leaved Silver Gum, Silver Gum (Tasmania) A somewhat variable but always beautiful tree of 18 to 80' tall in habitat, it grows into a very straight upright tree in cultivation.  This species made especially attractive by the whitish-silver juvenile leaves which do not give way to willowy adult foliage even as the tree gets very tall.  Only near the tops of very old, large trees are the longer mature leaves seen.  The smooth bark is also attractive, and is predominantly white but may also have blue, purple and green on it.  May have round or square stems.  Considered one of the best for coastal planting, serving as an unsurpassable shelter tree; it also tolerates summer frosts better than many species.  8 to 13°F.
Photos of Eucalyptus cordata

Eucalyptus cosmophylla - Cup Gum, Bog Gum (South Australia) Small tree with smooth bark; tolerates waterlogged soil.  One of South Australia's hardiest eucs. 12 to 18°F.

Eucalyptus crenulata - Buxton Gum, Buxton Silver Gum, Silver Gum, Victorian Silver Gum (Victoria)  This small tree of moderate to fast growth is under-rated in cultivation for its many uses.  It has smooth bark and small, silvery leaves with crenulated margins (hence "crenulata").  The white flowers are not showy on the tree, but interesting to look at and sweet-smelling up close.  This species has potential for use in the cut foliage industry, being extremely productive; and is less prone to insect damage than many other species in areas where this is a problem.  Very useful in cold, wet, yukky areas - probably not too drought-tolerant, but does well in waterlogged soil.  One of the most shade tolerant eucs along with E. neglecta.  Grows to about 30' high.  Rare in the wild; extremely fine seed.  1 to 8°F.
Photos of Eucalyptus crenulata

Eucalyptus cunninghamii (New South Wales) An extremely rare, diminutive, brushy looking mallee from restricted areas of New South Wales.  Quite hardy.
Photos of Eucalyptus cunninghamii

Eucalyptus cypellocarpa - Mountain Grey Gum, Monkey Gum, Spotted Mountain Gum, Spotted Mountain Grey Gum, Small-fruited Mountain Gum, Mountain Blue Gum, Mountain Gum (Australia) A tall, fast-growing, blue leaved species, closely related to E. nitens but even more fussy about its requirements for a cool moist site and shelter from severe frost.  12 to 17°F.
Photos of Eucalyptus cypellocarpa