Leaves: Cotyledons—sessile to slightly conjoined at base, elliptical; to 0.5 X 0.25 cm; hypocotyl reddish and minutely hairy. Seedling—deciduous and persistent branches similar in morphology, whorls of 4 leaf teeth closely appressed to the branch at the joint, gradually increasing in number, internodes (articles) 0.3-0.4 cm long. Adult—deciduous and permanent branches noticeably different in morphology, deciduous branches robust, dark olive-green to grey, mostly pendent branchlets 10-20 cm long, shed after 2-3 seasons, leaf teeth in whorls of 9-16, internodes (articles) about 0.7-1.5 cm long, teeth erect, appressed, articles 0.6-0.9 mm diameter, occasionally sparsely pubescent (cristata) or teeth spreading to recurved, articles 1-1.8 mm diameter, densely pubescent ( pauper).
Inflorescences: Male and female on separate trees. Male— flowers on small slender terminal spikes at the end of deciduous branches. Female—grouped in alternating whorls of 9-16 flowers, eventually forming a cone which is grey, subspherical to rounded oblong in shape, 1.5-3 X 1.5-2.5 cm nearly sessile on stalks 0.1-0.3 cm long, bracteoles relatively thin, triangular, protruding, 0.3-0.4 X 0.3-0.4 cm (cristata) or shorter and tawny-pubescent (pauper) and opening widely at dehiscence; backs of individual bracteoles can have long striations running down from the apex.
Fruits: Samaras, dull yellow-brown, elliptical, flattened, up to 0.6 X 0.2 cm, papery transparent wing with conspicuous midrib.
Wood: Sapwood is wide and creamy coloured, Lyctus susceptibility unknown; heartwood is reddish brown, fissile, very dense, density 1100 kg m-3. The wood is used for fencing and makes good fuel; poles are used for building stockyards. The wood is excellent for turnery.
Climate: Altitudinal range: 400-500 m; Hottest/coldest month: 30-35°C/1-5°C (cristata), 32-36°C/3-7°C (pauper); Frost incidence: moderate; Rainfall: 450-650 mm per year (cristata), 200-350 mm per year (pauper) mm per year, mainly summer max. (cristata), mainly winter max. (pauper).
Distinctive features: Arborescent casuarinas with hard bark and fruits with pointed bracteoles protruding from the cone.
Casuarina cristata 1. Cones before dehiscence 2. Cones after dehiscence 3. Seedling 4. Male inflorescence 5. Male flower showing anther (S.E.M.) 6. Adult branchlets with male inflorescences at ends 7. Leaf teeth at joint (S.E.M.) 8. Bark 9. Trees of C. cristata between Naromine and Nyngan, N.S.W. 10. Trees of C. pauper between Kalgoorlie and Coolgardie, W.A. 11. Bark
River Oak River Sheoak, Creek Oak (Qld)
River oak is usually a medium-sized to tall tree attaining 20-35 m in height and 0.5-1.5 m in diameter. It is the largest species of the genus in Australia, although in open country in the north of the area of occurrence, such as south-east of the Gulf of Carpentaria in Queensland and in the Northern Territory, it may be only 12 m in height and straggly in appearance. There are two subspecies, the typical and subsp. miodon.
Subsp. cunninghamiana occurs in narrow belts along permanent freshwater watercourses throughout eastern Australia from Bega, southern New South Wales to the Laura basin in northern Queensland. It extends inland to east of Chillagoe and Augathella in Queensland and to Condobolin and west of Narrandera in New South Wales. Subsp. miodon grows along fresh or brackish permanent streams and extends east from the Daly River, Northern Territory to the Gulf of Carpentaria, Queensland.
River oak mainly grows as pure stands on river and stream banks in open forests, especially in the belt between normal water level and maximum flood level, and occasionally on adjacent river flats. The species may extend for a short distance up rocky hillsides, chiefly on limestone. The soils range from fine-textured sands through to gravels in terraces of old river courses. In the typical riverine location the roots have access to flowing water or seepage.
The tree is used for ornamental planting, for shade and shelter and shows an ability to grow satisfactorily on comparatively dry soils. The foliage, particularly of seedlings, is a usable drought fodder.
Related species: Of the species occurring in eastern Australia river oak is closely related to C. glauca. It differs from this species in its preference for sites where the groundwater is fresh rather than salt or brackish, its fewer teeth per whorl (8-10 versus 12-16) and its shorter, thinner branchlets. Occasional intermediate forms, considered to be hybrids, occur where the habitats of the two species meet, e.g. near Wisemans Ferry, New South Wales.
Publication: Subsp. cunninghamiana: Rev. Crit. Casuar. 56, t. 6A (1848). Type: Sandy shores of Moreton Bay and Glasshouse Bay, Queensland, collector unknown. Subsp. miodon: Fl. Austral. 3, 200 (1989). Type: 23 km NNE of Borroloola on Bing Bong road, Northern Territory, 13 May 1983, K.L. Wilson 5361.
Names: Botanical—after A. Cunningham (1791-1839), an explorer and botanical collector mainly in eastern Australia. Common—alludes to the habitat on river banks, and the conspicuous medullary rays which reminded the early settlers of true oaks (Quercus spp.).
Bark: Persistent over the whole of the trunk and branches, dark grey, hard, deeply furrowed longitudinally and irregularly in a transverse direction. On young trees the numerous raised white, horizontally disposed, lenticel-like pustules are conspicuous.
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