Including Agialidaceae Van Tieghem
Habit and leaf form. Small trees, or shrubs (with axillary, simple or forked spines and bitter bark); non-laticiferous and without coloured juice. Leaves alternate; leathery; petiolate; non-sheathing; not gland-dotted; compound; bifoliolate; exstipulate. Lamina margins entire.
Leaf anatomy. Stomata present; anomocytic.
Stem anatomy. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. ‘Included’ phloem absent. Xylem with fibre tracheids. Vessel end-walls simple. Primary medullary rays wide. Wood partially storied (VP); parenchyma apotracheal.
Reproductive type, pollination. Plants hermaphrodite.
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’. Inflorescences axillary. Flowers fragrant; regular; 5 merous; cyclic. Free hypanthium absent. Hypogynous disk present; intrastaminal; annular (cupular or cushion shaped, 10-grooved).
Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; polysepalous; regular; not persistent; slightly imbricate. Corolla 5; 1 whorled; polypetalous (the petals spreading); imbricate; regular; green (-ish). Petals sessile.
Androecium 10. Androecial members free of the perianth; free of one another. Androecium exclusively of fertile stamens. Stamens 10; diplostemonous; both alternating with and opposite the corolla members; filantherous (the filaments filiform). Anthers dorsifixed; tetrasporangiate. Endothecium developing fibrous thickenings. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral, or decussate. Anther wall initially with more than one middle layer; of the ‘monocot’ type. Tapetum glandular. Pollen grains aperturate; 3 and 6 aperturate; colporate and rugate (tricolporate and 6-rugorate); 2-celled.
Gynoecium 5 carpelled. Carpels isomerous with the perianth. The pistil 5 celled. Gynoecium syncarpous; eu-syncarpous; superior to partly inferior (semi-immersed in the disk). Ovary 5 locular; sessile. Gynoecium stylate. Styles 1; attenuate from the ovary; apical; shorter than the ovary (very short, subulate). Stigmas 1; minute. Placentation axile to apical. Ovules 1 per locule; funicled; pendulous; hemianatropous; bitegmic; crassinucellate. Outer integument contributing to the micropyle. Endothelium differentiated. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization, or fusing only after one has been fertilized (?). Antipodal cells formed; 3; not proliferating; ephemeral. Synergids hooked. Endosperm formation nuclear.
Fruit fleshy; indehiscent; a drupe (fleshy, oily, the endocarp bony and 5-angled). The drupes with one stone. Fruit 1 seeded (and unilocular). Seeds non-endospermic. Embryo well differentiated. Cotyledons 2 (thick, corrugated or bilobed). Embryo chlorophyllous. Micropyle zigzag.
Geography, cytology. Paleotropical. Tropical. Tropical Africa to Burma.
Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Rutiflorae; Geraniales. Cronquist’s Subclass Rosidae; Sapindales. APG (1998) Eudicot; core Eudicot; Rosid; unassigned to Eurosid I or Eurosid II. APG 3 (2009) Order: Fabales.
Species 25. Genera 1; only genus, Balanites.
• Technical details: Balanites (Thonner).