Habit and leaf form. Small shrubs, or herbs. Young stems often tetragonal. Helophytic, or mesophytic. Leaves opposite; sometimes somewhat turgescent; petiolate (petiole generally short); simple. Leaf blades entire; lanceolate, or oblong, or ovate; elliptic, or ovate, or linear; 3–7 -nerved; palmately veined and parallel-veined (no dominant midrib, the several strong veins diverging at the base, converging at the apex); cross-venulate. Leaves without stipules. Leaf blade margins entire, or serrate. Leaves without a persistent basal meristem. Stem anatomy. Secondary thickening absent, or developing from a conventional cambial ring, or anomalous; from a single cambial ring.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Floral nectaries present, or absent. Nectar secretion from the perianth, or from the androecium. Entomophilous, or ornithophilous, or cheiropterophilous.
Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’; in cymes, or in fascicles (or clusters). The terminal inflorescence unit cymose. Inflorescences terminal, or axillary; inflorescence usually clustered, rarely an elongated cyme or flowers solitary. Flowers usually pedicellate; bracteate; bracteolate; operculate (calyptrate), or not operculate; regular, or somewhat irregular. The floral asymmetry involving the androecium. Flowers 3–5(–6) merous; tetracyclic, or pentacyclic. Free hypanthium present; campanulate, or urceolate; usually moderately to densely covered with emergences or hairs or both; adnate to the ovary in the lower half by longitudinal septa. Perianth with distinct calyx and corolla; 8–10(–12); 2 -whorled; isomerous. Calyx present; 4–5(–6); 1 -whorled; gamosepalous; blunt-lobed; calyptrate, or not calyptrate; imbricate, or valvate, or contorted, or open in bud; regular; not persistent. Calyx lobes elliptic, or ovate, or triangular. Corolla present; 4–5(–6); 1 -whorled; polypetalous; contorted; regular; white, or red, or pink, or purple, or blue. Petals obovate, or orbicular. Androecial members definite in number. Androecium 8, or 10–12. Androecial members free of the perianth; all equal, or markedly unequal (rarely); free of one another; 1 -whorled, or 2 -whorled. Stamens 8, or 10(–12); all more or less similar in shape, or distinctly dissimilar in shape (rarely); diplostemonous; inflexed in bud; filantherous. Anthers basifixed; non-versatile; dehiscing via pores; initially tetrasporangiate; appendaged, or unappendaged. Gynoecium 4–5(–6) carpelled. The pistil 4–5(–6) celled. Gynoecium syncarpous; eu-syncarpous; partly inferior. Ovary plurilocular; 4–5(–6) locular. Epigynous disk absent. Gynoecium stylate. Styles 1; apical. Stigmas 1. Placentation axile. Ovules (2–)6–50 per locule; anatropous.
Fruit and seed features. Fruit non-fleshy; dehiscent; a capsule. Capsules loculicidal. Fruit 20–100 seeded. Seeds non-endospermic; small. Embryo well differentiated (but minute). Cotyledons 2. Micropyle zigzag.
Special features. Larger stamens without a distinct connective prolongation.
Etymology. After Pehr Osbeck (1723–1805), Swedish ship's chaplain and botanist who travelled in China and the East Indies and presented his collection of 600 Chinese plants to Linnaeus.
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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/