Common name. Sheoaks. Family Casuarinaceae.
Habit and leaf form. Trees (with ‘equisetiform’ shoots). Switch-plants; with the principal photosynthesizing function transferred to stems. Leaves much reduced. Leaves cauline. Leptocaul. Helophytic to xerophytic. Leaves minute; whorled; 5–20 per whorl; membranous; sessile; connate; simple. Leaf blades entire. Leaves without stipules. Stem anatomy. 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 segregated in different inflorescences. Female flowers without staminodes. Anemophilous.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in spikes, or in heads. Inflorescences when male, simple elongate spikes; when female, on short lateral branchlets differing in appearance from the vegetative branchlets. The fruiting inflorescence conelike. Flowers bracteate; bracteolate; small. Hypogynous disk absent. Perianth vestigial (male flowers), or absent (females); 1–2 (of scales). Fertile stamens present, or absent. Androecial members definite in number. 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, or absent. Gynoecium 2 carpelled. The pistil 2 celled. Gynoecium syncarpous; synstylovarious; superior. Ovary plurilocular; 2 locular. Gynoecium stylate. Styles 1; apical. Stigmas 2. Ovules 2 per 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. The multiple fruits not coalescing. Seeds non-endospermic. Embryo well differentiated. Cotyledons 2 (oily). Embryo straight.
Etymology. From Malay casuari (cassowary); a bird like an ostrich; refers to the resemblance of the drooping branches to the feathers of the bird.