Osbornia F.Muell.

Scientific Description

Common name. Myrtle Mangroves. Family Myrtaceae.

Habit and leaf form. Trees, or shrubs; evergreen; bearing essential oils. Plants with neither basal nor terminal concentrations of leaves; to 5(–9) m high. Leptocaul. Helophytic. Leaves small to medium-sized; opposite; decussate; ‘herbaceous’, or leathery; petiolate to sessile; 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; obovate, or oblong; pinnately veined, or parallel-veined, or one-veined; cross-venulate, or without cross-venules. Mature leaf blades adaxially glabrous; abaxially glabrous. Leaves without stipules; without a persistent basal meristem. Leaf anatomy. Hairs absent. 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 solitary, or aggregated in ‘inflorescences’; axillary. The terminal inflorescence unit cymose. Inflorescences axillary; of 1(-3) flowers. Flowers pedicellate, or sessile; bracteolate. Bracteoles deciduous. Flowers small; regular; 8 merous; cyclic. Free hypanthium present; obconic, or turbinate; not extending beyond ovary; hairy. Perianth sepaline; 8; 1 -whorled; joined (below); sepaloid; hairy; white; persistent. Perianth members entire. Calyx present; 8; 1 -whorled; polysepalous; erect; imbricate, or valvate; white; persistent. Sepals ovate. Corolla absent. Androecial members indefinite in number. Androecium 20–100 (ie. ‘numerous’). Androecial members branched. Androecial sequence determinable, or not determinable. Androecial members maturing centripetally; free of the perianth; all equal; free of one another. Stamens 20–100 (ie. ‘numerous’); attached on the rim of the hypanthium; becoming exserted (exceeding the sepals); all more or less similar in shape; polystemonous; alternisepalous and oppositisepalous (with loss of some antesepalous members?); erect in bud, or inflexed in bud. Filaments filiform. Anthers all alike; dorsifixed; versatile; dehiscing via longitudinal slits; introrse; tetrasporangiate; appendaged, or unappendaged. Gynoecium 2 carpelled. The pistil 1 celled, or 2 celled (imperfectly). Gynoecium syncarpous; synstylovarious to eu-syncarpous; inferior. Ovary unilocular, or plurilocular; 1 locular, or 2 locular. Epigynous disk present. Gynoecium stylate. Styles 1; apical; becoming exserted; persistent; hairy (on basal half). Stigmas 1. Placentation when unilocular, basal; basal. Ovules in the single cavity 20–50 (i.e. ‘numerous’); 20–50 per locule (i.e. ‘numerous’); ascending; non-arillate; anatropous.

Fruit and seed features. Fruit non-fleshy; indehiscent (enclosed in the somewhat enlarged hypanthium); a berry, or a drupe, or a nut; 1 seeded, or 2 seeded. Seeds non-endospermic; obovoid. Cotyledons 2; thick and flattened or hemispherical, longer than the radicle. Embryo straight.

Special features. Mangroves (but without pneumatophores).

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.