Family Octoknemaceae

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. Stomata present; mainly confined to one surface (abaxial); anomocytic. Hairs present; multicellular. Complex hairs present; stellate (or fasciculate).

Lamina dorsiventral (the adaxial mesophyll more compact).

Stem anatomy. Cork cambium present; initially superficial. The cortex containing cristarque cells, or without cristarque cells. Cortical bundles absent. Medullary bundles absent. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. ‘Included’ phloem absent. Xylem without fibre tracheids; with libriform fibres. Vessel end-walls scalariform (Okoubaka), or simple (Octoknema). Vessels without vestured pits. Wood parenchyma apotracheal (and diffuse, in Okoubaka, absent in Octoknema). Pith with diaphragms, or without diaphragms.

Reproductive type, pollination. Fertile flowers functionally male, or functionally female. 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 unit 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, biochemistry. 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 3 core angiosperms; core eudicot; Superorder Santalanae; Order Santalales (as a synonym of Olacaceae).

Species 8. Genera 2; Octoknema, Okoubaka.

This description is very inadequate: mostly quoted from Airy Shaw (1973), and differing considerably from that of Hutchinson (1960).