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The families of flowering plants

L. Watson and M.J. Dallwitz

Oncothecaceae Kobuski ex Airy Shaw

Habit and leaf form. Small, ‘crescent-shaped’ trees, or shrubs. Leaves persistent; alternate (crowded towards the branch tips); spiral; leathery; petiolate to subsessile; non-sheathing; simple. Lamina entire; oblanceolate; pinnately veined; cross-venulate; attenuate to the base. Leaves exstipulate. Lamina margins entire, or dentate (then only minutely glandular-denticulate towards the apex).

Leaf anatomy. The leaf lamina more or less bifacial (bifacial). Stomata present; mainly confined to one surface (abaxial); anomocytic, or paracytic, or tetracytic (nearly anomocytic, tending to the others). Adaxial hypodermis present. The mesophyll with sclerenchymatous idioblasts; containing crystals. The crystals druses.

Axial (stem, wood) anatomy. Cork cambium present; initially superficial (in the outer cortex). Nodes penta-lacunar. Secondary thickening developing from a conventional cambial ring.

The vessel end-walls oblique; exclusively scalariform. The axial xylem with tracheids, or without tracheids (the latter according to Carpenter and Dickison); with fibre tracheids (according to Carpenter and Dickison). The parenchyma apotracheal and paratracheal (diffuse to diffuse in aggregates, and scanty).

Reproductive type, pollination. Plants hermaphrodite.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in panicles (thyrsoid). The ultimate inflorescence units cymose. Inflorescences axillary (towards the branch tips); ‘in more or less narrow axillary thyrses with angular rachides’ (Airy Shaw 1973), the pedicels very short. Flowers (one-) bracteate (more or less sessile); (bi-) bracteolate; small; regular; 5 merous; cyclic; tetracyclic. Free hypanthium absent. Hypogynous disk seemingly absent (never mentioned).

Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; polysepalous (McPherson 1981); regular; persistent; much imbricate (quincuncial). Corolla 5; 1 whorled; gamopetalous; imbricate (the lobes rounded); shortly campanulate; regular; deciduous. Petals sessile.

Androecium 5. Androecial members adnate (to the corolla tube); free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens 5; isomerous with the perianth; oppositisepalous (by contrast with Ebenaceae); alternating with the corolla members; filantherous (the filaments short). Anthers basifixed (with a thick connective); non-versatile; dehiscing via longitudinal slits; extrorse; bilocular; said to be bisporangiate; appendaged (O. balansae), or unappendaged (O. macrocarpa). The anther appendages of O. balansae apical (the connectives prolonged and abruptly inflexed, the five thus forming a roof over the gynoecium). Pollen shed as single grains. Pollen grains aperturate; 3 aperturate; colporate.

Gynoecium 5 carpelled. Carpels isomerous with the perianth. The pistil 5 celled. Gynoecium syncarpous; synovarious (shortly five lobed, each lobe ventrally stigmatic and imperfectly sealed); superior. Ovary 5 locular (and five-grooved). Gynoecium shortly stylate. Styles 5 (short, recurved); free; apical; shorter than the ovary. Stigmas 3. Placentation axile to apical. Ovules 1–2 per locule; long funicled; pendulous; epitropous; when paired, collateral; non-arillate; anatropous; unitegmic; crassinucellate (?).

Fruit fleshy; indehiscent; a drupe (oblate-compressed, with thin flesh). The drupes with one stone (this very thick walled, 5–locular). Fruit 2–5 seeded. Seeds copiously endospermic. Embryo well differentiated. Cotyledons 2(–3) (very short). Embryo straight.

Geography, cytology. Paleotropical. Tropical. New Caledonia.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli (ovule dubiously crassinucellate, unitegmic; exstipulate, gamopetalous, etc.). Dahlgren’s Superorder Theiflorae; Theales. Cronquist’s Subclass Dilleniidae; Theales. APG III core angiosperms; core eudicot; Superorder Asteranae; lamiid. APG IV Order Garryales.

Species 2 (Oncotheca humboldtiana, O. balansae). Genera 1; only genus, Oncotheca.

General remarks. See Carpenter and Dickison 1976.

Illustrations. • Oncotheca balansae and O. macrocarpa: McPherson, Bull. du Mus. Nat. d'Histoire Nat. Adansonia, Sect. B (1981).

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 15th April 2018.’.