Habit and leaf form. Trees and shrubs (with `equisetiform' shoots). Switch-plants; with the principal photosynthesizing function transferred to stems. Leaves much reduced. Leptocaul. Helophytic to xerophytic. Leaves minute; whorled; 4-12 per whorl; membranous; sessile; connate; aromatic (at least, the shoots so in Allocasuarina), or without marked odour; simple; exstipulate.
General anatomy. Accumulated starch exclusively `pteridophyte type'.
Leaf anatomy. Minor leaf veins without phloem transfer cells.
Stem anatomy. Cork cambium present. Nodes unilacunar. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. `Included' phloem absent. Xylem with fibre tracheids; with vessels. Vessel end-walls scalariform, or scalariform and simple. Vessels without vestured pits. Sieve-tube plastids S-type.
Reproductive type, pollination. Monoecious, or dioecious. Anemophilous.
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in `inflorescences'; in spikes, in heads, in glomerules, and in catkins. Inflorescences catkins, with males in simple or compound spikes, females in spherical or ovoid heads maturing into woody `cones'. Flowers bracteate (the bracts becoming woody in the female); bracteolate (the bracteoles becoming woody in the female); small. Hypogynous disk absent.
Perianth vestigial (male flowers), or absent (females); when present (male flowers), 1, or 2 (small).
Androecium 1. Androecial members unbranched (but tending to split); adnate. Androecium exclusively of fertile stamens. Stamens 1. Anthers basifixed; dehiscing via longitudinal slits. Endothecium developing fibrous thickenings. The initial microspore tetrads tetrahedral. Anther wall initially with more than one middle layer. Pollen grains aperturate; (2-)3(-5) - aperturate; porate; 2-celled.
Gynoecium 2; syncarpous; synstylovarious; superior. Ovary 2 locular (one of them abortive). Styles 1; apical. Stigmas 2. Ovules 2 per locule (in the fertile locule); collateral; non-arillate; orthotropous; bitegmic; crassinucellate. Outer integument not contributing to the micropyle. Embryo-sac development Polygonum-type. Polar nuclei fusing only after one has been fertilized, or fusing simultaneously with the male gamete (?). Antipodal cells formed; 3; not proliferating; ephemeral. Endosperm formation nuclear.
Fruit non-fleshy; indehiscent; a nut and a samara (single seeded, terminally winged). Fruits from adjoining flowers aggregated into compound fruits (cones). Seeds non-endospermic. Seeds without starch (oil and protein only). Embryo well differentiated. Cotyledons 2 (oily). Embryo straight.
Seedling. Germination phanerocotylar.
Nitrogen-fixing root nodules present (commonly), or absent. Physiology, biochemistry. Not cyanogenic. Alkaloids absent (11 species). Iridoids absent. Proanthocyanidins present; cyanidin, or delphinidin. Flavonols present, or absent; when present, kaempferol and quercetin. Ellagic acid present, or absent (2 species listed). Saponins/sapogenins absent (?). Aluminium accumulation not found. C3. C3 recorded in Casuarina.
Geography, cytology. Temperate to tropical. Australia, Malaysia, New Caledonia, Fiji, Mascarene Is. X = 8-14. Supposed basic chromosome number of family 9 (?).
Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren's Superorder Rosiflorae; Casuarinales. Cronquist's Subclass Hamamelidae; Casuarinales. Takhtajan's Subclass Hamamelidae; Hamamelidanae; Casuarinales. Species 65. Genera 4; Allocasuarina, Casuarina, Ceuthostoma, Gymnostoma.
Economic uses, etc. Timber trees (`she-oak') where indigenous, and cultivated as ornamentals in warm regions elsewhere.
Illustrations. casua684.gif
Additional, to be intercalated. The fruiting inflorescences conelike.
