Habit and leaf form. Trees, or shrubs; evergreen; bearing essential oils. Plants with neither basal nor terminal concentrations of leaves. Young stems cylindrical, or tetragonal (or 4-winged, usually glabrous). To 2–35 m high. Leptocaul. Helophytic to mesophytic. Leaves medium-sized to large; opposite; decussate; ‘herbaceous’, or leathery; petiolate to subsessile; gland-dotted; aromatic; edgewise to the stem, or with ‘normal’ orientation; simple; epulvinate. Leaf blades dorsiventral, or isobilateral, or centric; entire; flat; linear, or lanceolate, or oblong, or ovate; linear, or ovate, or obovate, or elliptic, or orbicular; pinnately veined, or parallel-veined, or one-veined; cross-venulate, or without cross-venules. Leaves without stipules; without a persistent basal meristem. Stem anatomy. Secondary thickening developing from a conventional cambial ring.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous, or ornithophilous. Pollination mechanism unspecialized.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’. Inflorescence few-flowered, or many-flowered. Flowers in cymes, or in racemes, or in umbels, or in panicles. Inflorescences simple, or compound. The terminal inflorescence unit cymose. Inflorescences terminal, or axillary; commonly a cyme or panicle of cymes. Flowers pedicellate; bracteate. Bracts persistent, or deciduous. Flowers (bi) bracteolate, or ebracteolate; small to medium-sized; operculate (calyptrate) (the operculum comprising the calyx alone or a structure incorporating both calyx and corolla), or not operculate; regular, or somewhat irregular; zygomorphic. The floral asymmetry (when noticeable) involving the perianth. Flowers 3–6 merous; cyclic. Free hypanthium present (petals ‘inserted on the calyx’). Perianth with distinct calyx and corolla (though these may be adnate to one another, forming an operculum which is shed at anthesis); 6–12; 2 -whorled; isomerous. Calyx present; (3–)4–5(–6); 1 -whorled; polysepalous, or gamosepalous; glabrous; calyptrate, or not calyptrate; not shed before the corolla; imbricate, or valvate; regular, or unequal but not bilabiate (in S. eucalyptoides and S. suborbiculare where the 2 inner lobes are larger than the outer pair); usually persistent (when free), or not persistent. Corolla present; (3–)4–5(–6); 1 -whorled; polypetalous, or gamopetalous; calyptrate (and adherent to the calyx), or not calyptrate; imbricate; regular; white, or cream; persistent, or deciduous. Petals orbicular. Androecial members indefinite in number. Androecium 50–150 (‘many’). Androecial members branched. Androecial sequence determinable, or not determinable. Androecial members maturing centripetally; free of the perianth; often markedly unequal, or all equal; free of one another. Stamens 100 (‘many’); becoming exserted (the longer ones exceeding the petals); polystemonous; alternisepalous and oppositisepalous; both opposite and alternating with the corolla members; erect in bud, or inflexed in bud. Anthers dorsifixed; versatile; dehiscing via longitudinal slits; introrse; tetrasporangiate; appendaged, or unappendaged. Gynoecium 2–3 carpelled. The pistil 2(–3) celled. Gynoecium syncarpous; eu-syncarpous; inferior. Ovary plurilocular; 2(–3) locular. Epigynous disk present. Gynoecium stylate. Styles 1; apical. Stigmas 1. Placentation axile (frequently condensed and confined to the middle of each locule). Ovules 5–65 per locule; horizontal to ascending, or pendulous (occasionally); non-arillate; anatropous.
Fruit and seed features. Fruit fleshy, or non-fleshy (rarely spongy to coriaceous or brittle); indehiscent; a berry; 2–3 celled; 1(–5) seeded. Seeds non-endospermic; winged, or wingless. Cotyledons 2; free from one another.
Special features. Corolla completely congenitally fused with the calyx, or not congenitally fused with the calyx.
Geography, cytology, number of species. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia, Northern Territory, and Queensland. Northern Botanical Province.
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Western Australian Herbarium (1998–). FloraBase—the Western Australian Flora. Department of Biodiversity, Conservation and Attractions. https://florabase.dpaw.wa.gov.au/