Casuarinaceae R.Br.

Scientific Description

Common name. Sheoak Family.

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 (the shoots pungent, in Allocasuarina), or without marked odour; simple; without stipules. Stem anatomy. Nodes unilacunar. Secondary thickening developing from a conventional cambial ring.

Reproductive type, pollination. Fertile flowers functionally male and functionally female, or functionally male, or functionally female. Unisexual flowers present. Plants monoecious, or dioecious. The unisexual flowers when monoecious, segregated in different inflorescences. Anemophilous.

Inflorescence and flower features. 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’. The fruiting inflorescence conelike. 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). Fertile stamens present (in male flowers), or absent (in females). Androecium 1. Androecial members unbranched (but tending to split); adnate. Androecium exclusively of fertile stamens. Stamens 1. Anthers basifixed; dehiscing via longitudinal slits. Fertile gynoecium present (female flowers), or absent (males). Gynoecium 2 carpelled. The pistil 1 celled, or 2 celled. Gynoecium syncarpous; synstylovarious; superior. Ovary plurilocular; 2 locular (one of them abortive). Styles 1; apical. Stigmas 2. Ovules 2 per locule (in the fertile locule); collateral; non-arillate; orthotropous.

Fruit and seed features. Fruit non-fleshy; indehiscent; a nut and a samara (single seeded, terminally winged). Gynoecia of adjoining flowers combining to form a multiple fruit (cones). Seeds non-endospermic; without starch (oil and protein only). Embryo well differentiated. Cotyledons 2 (oily). Embryo straight. Seedling. Germination phanerocotylar.

Physiology, biochemistry. Nitrogen-fixing root nodules present (commonly), or absent. Aluminium accumulation not found. Photosynthetic pathway: C₃.

Geography, cytology, number of species. World distribution: Australia, Malaysia, New Caledonia, Fiji, Mascarene Is. X = 8–14. 65 species.

Economic uses, etc. Timber trees (‘she-oak’) where indigenous, and cultivated as ornamentals in warm regions elsewhere.