Hypocalymma longifolium, commonly known as long-leaved myrtle,[1] 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 . Its leaves are arranged in opposite pairs, glabrous, linear, long, wide and deeply convex on the lower surface. The flowers are mostly borne in pairs in leaf axils and are in diameter, sessile or on a peduncle up to long. The flowers are white or cream-coloured, sessile or on a pedicel up to long. The sepal lobes are broadly egg-shaped or very broadly egg-shaped, long and wide. There are 40 to 50 stamens in several rows, the longest filaments long. Flowering occurs in August and September and the fruit is long and wide.
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.[2] [3] The specific epithet (longifolium) means 'long-leaved'.[4]
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.
Hypocalymma longifolium is listed as "Threatened Flora (Declared Rare Flora — Extant)" by the Government of Western Australia Department of Biodiversity, Conservation and Attractions.[5]