Strid & Keighery Hypocalymma longifolium, commonly known as long-leaved myrtle,[2] is a species of flowering plant in the myrtle family Myrtaceae, and is endemic to a restricted part of Western Australia.

It is an open shrub with linear leaves, and white or cream-coloured flowers arranged in pairs in leaf axils, with 40 to 50 stamens in several rows.

Hypocalymma longifolium' is an open shrub with many branches and that typically grows to a height of up to 1 m (3 ft 3 in).

[2][3] Hypocalymma longifolium was first formally described in 1860 by Ferdinand von Mueller in his Fragmenta Phytographiae Australiae from specimens near the Murchison River, collected by Augustus Oldfield.

[6] This species of Hypocalymma is found in a small area along the west coast in swamps or breakaways near the lower Murchison River, including in Kalbarri National Park, where it grows in sandy to clay soils.