Eucalyptus spathulata, commonly known as swamp mallet, narrow leaved gimlet or swamp gimlet, is a species of mallet that is endemic to Western Australia. It has a dense crown, smooth, satin-like bark, glossy green, linear leaves, flower buds in groups of three or seven, white flowers and cup-shaped to conical fruit.
Eucalyptus spathulata is a low-branching mallet with a dense crown that typically grows to a height of 8–12 m (26–39 ft) but does not form a lignotuber. The trunk usually has a diameter of 1–2 m (3 ft 3 in–6 ft 7 in) but can be even larger for older trees, and it is usually relatively short, sometimes fluted at the base. The bark is smooth, satin-like, greyish brown or reddish brown on the trunk and branches. Young plants have linear leaves that are 35–50 mm (1.4–2.0 in) long and 3–5 mm (0.12–0.20 in) wide and sessile or have a short petiole. Adult leaves are linear, the same shade of glossy green on both sides, 35–95 mm (1.4–3.7 in) long and 2–6 mm (0.079–0.236 in) wide, tapering to a petiole 1–7 mm (0.039–0.276 in) long. The flowers are arranged in leaf axils in groups of three or seven on an unbranched peduncle 3–15 mm (0.12–0.59 in) long, the individual buds on pedicels 2–6 mm (0.079–0.236 in) long. Mature buds are oval to spindle-shaped, 10–13 mm (0.39–0.51 in) long and 3–5 mm (0.12–0.20 in) wide with a horn-shaped or conical operculum two or three times as long as the floral cup. Flowering occurs between December and March and the flowers are white. The fruit is a woody cup-shaped to conical capsule 3–8 mm (0.12–0.31 in) long and 4–7 mm (0.16–0.28 in) wide with the valves near rim level.