Tree to 8 m. Branchlets up to 20 cm long, articles 0.4–1.7 cm long, smooth and glabrous, dull mid-green; phyllichnia flat, rounded or angled. Leaves tooth-like; teeth seven to nine, apressed or spreading, 0.08–0.15 cm long or to 0.35 cm long in juvenile growth. Dioecious; staminate inflorescences spicate, 0.75–1.3 cm long with six to eight whorls, early deciduous; pistillate inflorescences on lateral branchlets 0.4–1 cm long; cone 1.5–6 × 1.2–2.5 cm, bracteoles triangular and protruding. Fruit a samara, 0.6–1 cm long, dark brown or black. Johnson & Morris 1994. Distribution AUSTRALIA: Tasmania, Snug Plains (only known from one location). Habitat Dry, sclerophyllous Eucalyptus forest at c.600 m asl. USDA Hardiness Zone 9. Conservation status Not evaluated (IUCN), but this species has a restricted distribution and might be threatened if the protected status of its only habitat was changed. Illustration Johnson & Morris 1994; NT131. Taxonomic note This species is very similar to A. monilifera (L.A.S. Johnson) L.A.S. Johnson, though the staminate inflorescences are shorter.
Discovered only a few years previously, Allocasuarina duncanii was first introduced to cultivation by Barry Unwin of Logan Botanic Garden from collections made (B. Unwin 160) during his visit to Tasmania in 1996. Several young plants are now established at Logan, the tallest having reached 2.4 m in 2006 and apparently growing steadily. They have already flowered and fruited, producing beautifully ornate cones. It is a great surprise to see a plant so redolent of tropical beaches growing in Galloway, but A. duncanii is also cultivated in Cornwall and should be tried elsewhere.