Allocasuarina portuensis

Allocasuarina portuensis is a slender, dioecious shrub that typically grows to a height of 3–5 m (9.8–16.4 ft) and has smooth bark. Its branchlets are spreading to drooping, up to 270 mm (11 in) long, the leaves reduced to erect or slightly overlapping, spreading to curved backwards, scale-like teeth 0.7–1.1 mm (0.03–0.04 in) long, arranged in whorls of seven or eight around the branchlets. The sections of branchlet between the leaf whorls are 13–20 mm (0.5–0.8 in) long and 0.8–1 mm (0.03–0.04 in) wide, usually with a faint, waxy bloom. Male flowers are arranged in spikes resembling a string of beads 50–100 mm (2–4 in) long, with about 3.5 to 4.5 whorls per cm (per 0.4 in), the anthers 0.8–1 mm (0.03–0.04 in) long. Female cones are borne on a peduncle 2–15 mm (0.08–0.6 in) long, the mature cones 12–15 mm (0.5–0.6 in) long and 8–10 mm (0.3–0.4 in) in diameter. The winged seeds (samaras) are dark brown and 4–5 mm (0.16–0.20 in) long. Nielsen Park she-oak resembles Allocasuarina rigida and A. diminuta, but both usually lack male flowers arranged like a string of beads. Allocasuarina littoralis occurs in the same area as A. portuensis, but the former is a tree with fissured bark, also lacking the unusual arrangement of its male flowers.

At the time of its discovery, only two male and six female plants were known, at six locations in the south-eastern part of Nielsen Park. It is likely that the species previously had a wider distribution, since the vegetation of Nielsen Park at the time of European settlement was widespread on the foreshore of Sydney Harbour, but has since been extensively cleared. At the time of its discovery, the species was growing in tall, closed woodland with Port Jackson fig (Ficus rubiginosa), smooth-barked apple (Angophora costata), blueberry ash (Elaeocarpus reticulatus) and cheese tree (Glochidion ferdinandi) in the canopy, and an understorey including Pittosporum revolutum, Kunzea ambigua and Monotoca elliptica. The original habitat was degraded by weeds, such as asparagus "fern" (Protasparagus densiflorus), wandering Jew (Tradescantia albiflora) and Lantana camara. The original vegetation may have been more sclerophyllous, the absence of recent wildfire allowing the presence of more mesophyllic species, such as Glochidion ferdinandi and Pittosporum revolutum.