Allocasuarina portuensis, commonly known as the Nielsen Park She-Oak, is an extremely rare plant growing in Sydney, Australia. Encountered as a shrub or small slender tree, up to 5 metres (16 feet) tall, it has green drooping branchlets up to 27 cm (10.5 in) in length. It is dioecious, that is, male and female flowers are borne on separate plants. Measuring 1.2–1.5 cm (0.47–0.59 in) long and 0.8–1 cm wide, the cones are perched on 0.2–1.5 cm long peduncles arising from the branchlets.