The families of flowering plants

L. Watson and M.J. Dallwitz

Octoknemaceae Van Tiegh.

~ Olacaceae.

Habit and leaf form. Trees and shrubs. Leaves alternate; petiolate; not gland-dotted; simple. Lamina entire; pinnately veined; cross-venulate. Leaves exstipulate. Lamina margins entire.

Leaf anatomy. The leaf lamina dorsiventral (the adaxial mesophyll more compact). Stomata present; mainly confined to one surface (abaxial); anomocytic. Hairs present; multicellular. Complex hairs present; stellate (or fasciculate).

Axial (stem, wood) anatomy. The cortex containing cristarque cells, or without cristarque cells. Pith with diaphragms, or without diaphragms; heterogeneous (with groups of stone cells). Cork cambium present; initially superficial. Primary vascular tissues in a cylinder, without separate bundles; collateral. Internal phloem absent. Cortical bundles absent. Medullary bundles absent. Secondary thickening developing from a conventional cambial ring.

The wood diffuse porous. The vessels small, or medium; exclusively solitary (Okoubaka), or solitary, radially paired, and in radial multiples (Octoknema). The vessel end-walls scalariform (Okoubaka), or simple (Octoknema). The vessels without vestured pits; without spiral thickening. The axial xylem with tracheids, or without tracheids; with vasicentric tracheids (in Okoubaka), or without vasicentric tracheids; with fibre tracheids (about the vessels, in Okoubaka), or without fibre tracheids; with libriform fibres; without septate fibres. The fibres without spiral thickening. The parenchyma apotracheal (and diffuse, in Okoubaka, absent in Octoknema). ‘Included’ phloem absent. The wood not storied.

Reproductive type, pollination. Plants dioecious. Female flowers with staminodes. Gynoecium of male flowers pistillodial to vestigial.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in racemes. The ultimate inflorescence units racemose. Inflorescences axillary. Flowers regular; cyclic. Free hypanthium absent.

Perianth with distinct calyx and corolla, or petaline; 5, or 10; 1 whorled, or 2 whorled; when both calyx and corolla present, isomerous. Calyx when developed, 5 (but often obsolete); polysepalous. Corolla 5; 1 whorled; polypetalous; valvate; regular; persistent.

Androecium of male flowers, 5. Androecial members free of the perianth; all equal; free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens 5; isomerous with the perianth; alternisepalous; opposite the corolla members. Anthers basifixed; dehiscing via longitudinal slits. Pollen grains aperturate; 3 aperturate; colporate (colporoidate).

Gynoecium 3 carpelled. Carpels reduced in number relative to the perianth. The pistil 1 celled. Gynoecium syncarpous; synstylovarious to eu-syncarpous; inferior. Ovary essentially 1 locular (the threadlike placenta reaching and adnate to the top of the ovary, cf. Medusandraceae). Epigynous disk absent. Gynoecium stylate. Styles 1; apical; shorter than the ovary (short and thick). Stigmas 3 (these broadly reflexed and irregularly lobulate). Placentation apical. Ovules in the single cavity 3; pendulous; anatropous. Antipodal cells formed; 3; not proliferating. Synergids beaked.

Fruit fleshy; indehiscent; a drupe. The drupes with one stone. Fruit 1 seeded. Seeds endospermic. Endosperm slightly ruminate. Embryo well differentiated (small). Cotyledons 2 (much shorter than the radicle).

Physiology, phytochemistry. Aluminium accumulation demonstrated (in all three species examined).

Geography, cytology. Paleotropical. Tropical. West tropical Africa.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Santaliflorae; Santalales. Cronquist’s Subclass Rosidae; Santalales. APG III core angiosperms; core eudicot; Superorder Santalanae. APG IV Order Santalales (as a synonym of Olacaceae).

Species 8. Genera 2; Octoknema, Okoubaka.

General remarks. This description is very inadequate: mostly quoted from Airy Shaw (1973), and differing considerably from that of Hutchinson (1960). Supposedly distinguishable from Olacaceae by almost obsolete or free sepals, fully inferior ovary with apical placentation, and “somewhat ruminate” endosperm.

Illustrations. • Octoknema affinis, O. klaineana and O. winkleri: Nat. Planzenfam. iv (1895). • Octoknema gabonensis: Hutchinson.

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: 5th March 2018.’.