Eucalyptus saligna, commonly known as the Sydney blue gum or blue gum, is a species of medium-sized to tall tree that is endemic to eastern Australia. It has rough, flaky bark near the base of the trunk, smooth bark above, lance-shaped to curved adult leaves, flower buds in groups of seven, nine or eleven, white flowers and cylindrical to conical or cup-shaped fruit.
Eucalyptus saligna is a tree with a straight trunk that typically grows to a height of 30–55 m (98–180 ft), rarely to 65 m (213 ft), a dbh of 2–2.5 m (6 ft 7 in–8 ft 2 in), and forms a lignotuber. The trunk has smooth pale grey or white bark with 1–4 m (3 ft 3 in–13 ft 1 in) of rough brownish bark at the base. Young plants and coppice regrowth have lance-shaped to egg-shaped or oblong leaves that are paler on the lower surface, 37–120 mm (1.5–4.7 in) long and 15–40 mm (0.59–1.57 in) wide. Adult leaves are arranged alternately, glossy green, paler on the lower surface, lance-shaped to curved, 90–190 mm (3.5–7.5 in) long and 15–40 mm (0.59–1.57 in) wide, on a petiole 15–30 mm (0.59–1.18 in) long. The flower buds are arranged in leaf axils in groups of seven, nine or eleven on an unbranched peduncle 5–15 mm (0.20–0.59 in) long, the individual buds sessile or on pedicels up to 5 mm (0.20 in) long. Mature buds are spindle-shaped, oval or diamond-shaped, 5–10 mm (0.20–0.39 in) long and 3–5 mm (0.12–0.20 in) wide with a conical or beaked operculum. Flowering occurs from December to March and the flowers are white. The fruit is a woody cylindrical, conical or cup-shaped capsule 4–9 mm (0.16–0.35 in) long and 4–7 mm (0.16–0.28 in) wide with the valves protruding above the rim.