The River Red Gum grows to 45 metres (148 ft) as a tall, frequently straight tree, but can develop a more twisted habit in drier conditions.[3]. It has smooth bark to the smaller branches ranging in colour from white and grey to red-brown, frequently with loose basal slabs in the lower trunk, and which it sheds in large plates or flakes or short ribbons. [4] [5]
The tree has a large, dense crown of long and narrow adult leaves, lanceolate or infrequently falcate in shape, 5 to 30 centimetres (2.0 to 11.8 in) long by 0.7 to 3.2 centimetres (0.28 to 1.26 in) wide, and grey to grey-green on both surfaces. Side veins are prominent and usually at 45° to the leaf mid-rib, and oil glands are numerous and located separate to the veins. [4] [6] [3] [7] [8] [9]
Its inflorescences comprise umbels of 7 to 11 flower buds located at the junction of leaves and stem, with the buds being of ovoid or globular shape and 0.6 to 1.1 centimetres (0.24 to 0.43 in) long by 0.3 to 0.6 centimetres (0.12 to 0.24 in) wide. Buds are green to yellow or cream, and have a prominent tip beak. Flowers are white to cream, and have been recorded in bloom within the range from June through to March. The fruit (gum-nuts) are brown, hemispherical in shape, 0.2 to 0.5 centimetres (0.079 to 0.197 in) long by 0.4 to 1.0 centimetre (0.16 to 0.39 in) wide, with a highly raised end-disk and 3 to 5 valves strongly exserted.[4][6]
River reds and many other eucalypts have an ominous nickname, "widow maker", as they have a habit of dropping large boughs (often half the diameter of the trunk) without warning.[10] This form of self-pruning may be a means of saving water or simply a result of their brittle wood. This is also an efficient way of attracting wildlife that live in the holes formed, which gives the red gum a source of natural fertiliser[citation needed].