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The families of flowering plants

L. Watson and M.J. Dallwitz

Balanitaceae Endl.

~ Zygophyllaceae.

Including Agialidaceae Van Tieghem

Habit and leaf form. Small trees, or shrubs (with axillary, simple or forked spines and bitter bark); non-laticiferous. Leaves alternate; leathery; petiolate; non-sheathing; not gland-dotted; compound; bifoliolate; exstipulate. Lamina margins entire.

Leaf anatomy. Stomata present; anomocytic.

Axial (stem, wood) anatomy. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. Primary medullary rays wide.

The vessel end-walls simple. The axial xylem with fibre tracheids. The parenchyma apotracheal. ‘Included’ phloem absent. The wood partially storied (VP).

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 III core angiosperms; core eudicot; Superorder Rosanae; fabid. APG IV Order Zygophyllales (as a synonym of Zygophyllaceae).

Species 25. Genera 1; only genus, Balanites.

General remarks. In addition to the exstipulate leaves, green corolla and drupaceous fruits, these compiled descriptions have Balanites differing from Zygophyllaceae sensu stricto (q.v.) in assorted characters relying on limited sampling: details of wood anatomy, the ‘monocot type’ anther wall, hooked synergids, zigzag micropyle and absence of mustard oils.

Illustrations. • Balanites aegyptiaca: Hutchinson. • Balanites aegyptiaca: Thonner.

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.’.