Oncothecaceae Kobuski ex Airy Shaw
Habit and leaf form. Small, ‘crescent-shaped’ trees, or shrubs. Leaves evergreen; alternate (crowded towards the branch tips); spiral; leathery; petiolate to subsessile; non-sheathing; simple. Lamina entire; oblanceolate; pinnately veined; cross-venulate; attenuate at the base. Leaves exstipulate. Lamina margins entire, or dentate (then only minutely glandular-denticulate towards the apex).
Leaf anatomy. Stomata present; mainly confined to one surface (abaxial); anomocytic, or paracytic, or tetracytic (nearly anomocytic, tending to the others).
Adaxial hypodermis present. Lamina more or less isobilateral (bifacial). The mesophyll with sclerencymatous idioblasts; containing calcium oxalate crystals. The mesophyll crystals druses.
Stem anatomy. Cork cambium present; initially superficial (in the outer cortex). Nodes penta-lacunar. Secondary thickening developing from a conventional cambial ring. Xylem with tracheids, or without tracheids (the latter according to Carpenter and Dickison); with fibre tracheids (according to Carpenter and Dickison). Vessel end-walls oblique; exclusively scalariform. Wood 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 unit 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 3 core angiosperms; core eudicot; Superorder Asteranae; lamiid; Order Garryales.
Species 2. Genera 1; only genus, Oncotheca.
Carpenter and Dickison 1976.