Description: Dioecious or monoecious trees or shrubs with slender wiry articulate branchlets.
Leaves reduced to teeth in whorls of 4–20, portion of branchlet between whorls of teeth termed an 'article'; articles with as many longitudinal ridges (phyllichnia) as there are teeth, separated by closed [or open] furrows.
Inflorescences of alternating whorls of tooth-like bracts; within each bract 2 lateral scale-like bracteoles and a single unisexual flower. Male inflorescences short to elongated catkin-like spikes. Female inflorescences small globose or ovoid heads on short lateral branchlets ('peduncles'). Male flowers with 1 or 2 hooded, scale-like tepals and 1 stamen; anther basifixed. Female flowers without perianth; carpels 2, fused, with 2 (rarely 4) ovules; style reddish, bifid. Female inflorescence developing into ± woody infructescence ('cone') with the 2 enlarged bracteoles of each flower forming 2 lateral valves, which open when the seed-like samara is ripe; exposed portion of bracts thin or slightly woody [or much thickened]; seed solitary.
Distribution and occurrence: World: 4 genera, 97 species, Australia, Pacific islands & South-East Asia. Australia: 3 genera, 68 species, all States.
Angiosperm Phylogeny Website (Family: Casuarinaceae, Order: Fagales)
Some species, especially of Casuarina, are planted as ornamentals or soil-stabilizers. Timber of various species has been used for shingles, bullock yokes, fuel, etc. The name 'sheoak' was given in allusion to the timber, which is oak-like in appearance but was considered inferior in strength to English Oak. Various insects, especially coccoids, form distinctive galls that may be mistaken for fruiting cones. In exposed maritime situations, individuals may be stunted, with very thick branchlets and more teeth than usual.
Note: keys and descriptions are based on dried specimens. Dried specimens show important differences from fresh material. The cone bracteoles are nearly always appressed to each other, enclosing the samara, when fresh; once the cone is removed from the plant, the bracteoles separate. Measurements of cone length do not include any sterile apex (mentioned separately if of significant size); cone body diameter does not include the portion of the bracteoles extending beyond the main body of the cone. The softer tissues of branchlets contract when dried, so that features such as angularity or convexity of ridges are emphasized in dried specimens.
Text by K. L. Wilson & L. A. S. Johnson (1990); edited KL Wilson (Feb 2017)
Branchlet, inflorescences, cone and samara in Casuarinaceae. A, Allocasuarina littoralis portion of branchlet, showing leaf 'teeth' at apex of article; B & C, Casuarina cunninghamiana dense male inflorescences; D, A. glareicola moniliform male inflorescence; E–G, Allocasuarina littoralis, E, female inflorescence; F, portion of cone, showing bract, bracteoles and dorsal protuberance on bracteoles; G, samara, showing wing and body of seed.
| ||Key to the genera|| |
|1||Mature samaras grey or yellow-brown, dull; bracteoles of fruiting cone thinly woody, prominent, extending well beyond the cone body, without dorsal protuberance; teeth 6–20||Casuarina|
|Mature samaras red-brown to black, shining; bracteoles of fruiting cone thickly woody and convex, mostly extending only slightly beyond the cone body, with a separate angular or divided dorsal protuberance; teeth 4–14||Allocasuarina|