It has weeping branches, smooth bark, pale green linear leaves, small white flowers and thin-walled fruit.

[2][3][4] This species was first formally described in 1920 by Cyril Tenison White and William Douglas Francis who gave it the name Agonis longifolia and published the description in the Botany Bulletin, Department of Agriculture, Queensland.

[1] In the same journal, Wilson changed the names of 2 subspecies of Leptospermum madidum to Aggreflorum longifolium and the names are accepted by Plants of the World Online: Subspecies longifolium is confined to Cape York Peninsula where it grows on the banks of creeks and rivers.

[2] Subspecies sativum is found along watercourses and in sandstone gullies in the Kimberley region of Western Australia and the northernmost parts of the Northern Territory.

[2][3] Aggreflorum longifolium is listed as "not threatened" by the Government of Western Australia Department of Biodiversity, Conservation and Attractions,[3] but subsp.