Eucalyptus tereticornis, commonly known as forest red gum, blue gum or red irongum, is a species of tree that is native to eastern Australia and southern New Guinea. It has smooth bark, lance-shaped to curved adult leaves, flower buds in groups of seven, nine or eleven, white flowers and hemispherical fruit. Description Eucalyptus tereticornis is a tree that typically grows to a height of and forms a lignotuber. The trunk is straight, usually unbranched for more than half of the total height of the tree and has a girth of up to dbh. Thereafter, limbs are unusually steeply inclined for a Eucalyptus species. The bark is shed in irregular sheets, resulting in a smooth trunk surface coloured in patches of white, grey and blue, corresponding to areas that shed their bark at different times. Young plants and coppice regrowth have dull bluish green, egg-shaped leaves that are long and wide. Adult leaves are the same shade of green on both sides, lance-shaped to curved, long and wide, tapering at the base to a petiole long. The flower buds are arranged in leaf axils in groups of seven, nine or eleven on an unbranched peduncle long, the individual buds on pedicels long. Mature buds are an elongated oval shape, long and wide with a conical to horn-shaped operculum that is much longer than the floral cup. Flowering has been recorded in most months and the flowers are white. The fruit is a woody, hemispherical capsule long and wide with the valves prominently protruding. Taxonomy and naming Eucalyptus tereticornis was first formally described 1795 by James Edward Smith in A Specimen of the Botany of New Holland from specimens collected in 1793 from Port Jackson by First Fleet surgeon and naturalist John White. (Smith's volume was the botanical part of Zoology and Botany of New Holland. The zoological part was written by George Shaw.) The specific epithet (tereticornis) is from the Latin words teres (becoming tereti- in the combined form) meaning "terete" and cornu meaning "horn", in reference to the horn-shaped operculum. In 1999 Ian Brooker and Andrew Slee described two subspecies and in 2013 Anthony Bean described a further two, and the names of these four subspecies are accepted by the Australian Plant Census: Eucalyptus tereticornis subsp. basaltica A.R.Bean has opercula that are not expanded at the base, juvenile leaves that are dull bluish, egg-shaped to round, up to one to