Eucalyptus cladocalyx F.Muell., Linnaea 25: 388 (1853). E. corynocalyx F.Muell., Fragm. 2: 43 (1860), nom. illeg. based on same types as E. cladocalyx. T: Marble Ra., S.A., Feb. 1852, C.Wilhelmi s.n. ; holo: MEL; iso: K. E. langii Maiden & Blakely, Crit. Revis. Eucalyptus 8: 72 (1929). T: cultivated at Litanga Stn, Lismore, Vic., Apr. 1921, P.R.H.St John s.n. ; holo: NSW, iso: CANB.
Tree to 35 m tall. Lignotuber absent but epicormic buds present up the stem. Bark smooth, mottled white, yellow, pink, orange, brown, pale grey, dark grey or blue grey, sometimes slightly powdery. Juvenile growth (coppice or wild seedling to 50 cm tall): stems round in cross-section; juvenile leaves always petiolate, opposite at lowest node then alternate, orbicular (often wider than long), deltoid to ovate, 2–6.5 cm long, 2–9 cm wide, apex round or emarginate, base truncate, discolorous, dull, blue-green to green. Adult leaves alternate, petiole 0.9–2.7 cm long; blade slightly falcate to lanceolate, 8–17 cm long, 1.2–3.2 cm wide, base usually tapering to petiole, strongly discolorous, glossy, darker green on upper side, paler below, side-veins at an acute or wider angle, densely to very densely reticulate, intramarginal vein parallel to and well removed from margin, oil glands small, obscure. Inflorescence axillary unbranched but borne on leafless sections of branchlets (ramiflorous), peduncles 0.8–2.2 cm long, buds 7, 9 or 11 per umbel, pedicels 0.3–0.7 cm long. Mature buds oblong (0.8–1.1 cm long, 0.4–0.5 cm wide), pale green, yellow to creamy, often longitudinally striate, scar present, operculum rounded, stamens inflexed, anthers cuboid to oblong, versatile, dorsifixed, dehiscing by longitudinal slits (non-confluent), style short, stigma blunt, locules 3 or 4, the placentae each with 4 vertical ovule rows in each locule. Flowers white. Fruit pedicellate (pedicels 0.2–0.7 cm long), urceolate or barrel-shaped, 0.7–1.5 cm long, 0.5–1 cm wide, often longitudinally ribbed, disc descending, valves 3 or 4, deeply enclosed. Seeds light grey to brown, 1.5–3 mm long, ovoid or flattened-ovoid, or pointed at one end, dorsal surface smooth, with or without a very narrowly flanged rim, hilum ventral. Cultivated seedlings (measured at ca node 10): cotyledons bilobed; stems square to rounded in cross-section; leaves always petiolate, opposite for 2 or 3 nodes then alternate, deltoid to ovate or orbicular (though often wider than long), 2.5–5.5 cm long, 2–6 cm wide, apex rounded to emaginate, dull, green at lowest nodes becoming grey to grey-green up stem.
Flowering has been recorded in January, March and December.Eucalyptus cladocalyx is widely planted on farms in southern Australia for shelter belts in zones where rainfall is suitable. It is often lopped at ca 1 metre above ground level and the wood used for posts and fuel. It has also been milled for timber for general construction, poles, and railway sleepers, and has some value in honey production. It is also sometimes planted as an ornamental tree. In Western Australia Eucalyptus cladocalyx has escaped from plantings and become naturalised (Hussey et al., 1997), for example at Pelican Point on the Swan River estuary, Perth, and is invading bushland near Esperance. In Victoria it has been recorded as naturalised near Connewarre on the Bellarine Peninsula. Carr et al. (1992) regard this species as an environmental weed in Victoria posing a serious risk to lowland grassland and grassy woodland, dry sclerophyll forest and woodland, riparian vegetation and vegetation on rock outcrops, stating that it is already widespread in small populations.
A small to tall tree of disjunct distribution in South Australia from lower and central-eastern Eyre Peninsula, Kangaroo Island and the Flinders Range. It is closely related to no other species and may be distinguished by the mottled bark somewhat like that of grey gums, the orbicular juvenile leaves, strongly discolorous adult leaves that are paler on the underside, and inflorescences on leafless portions of branchlets inside the crown. It is probably a relic of tall forests of wetter climates in the distant past, although its morphological characters do not associate it with current wet forest species such as E. diversicolor and E. saligna. Eucalyptus cladocalyx belongs in Eucalyptus subgenus Symphyomyrtus because buds have two opercula and ovules are in four rows. Within this subgenus E. cladocalyx is somewhat isolated as the only species in section Sejunctae by the combination of its unusual inflorescence arrangement, discolorous leaves, absence of pith glands, bilobed cotyledons and flattened-ovoid seeds. Dean Nicolle in his book Native eucalypts of South Australia (2013), formally describes two subspecies of E. cladocalyx, subsp. crassa and subsp. petila. These are yet to be included in EUCLID and the reader is referred to the book for details.