| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Zygophyllaceae R. Br.

Including Tribulaceae Trautv., Tetradiclidaceae; excluding Balanitaceae, Nitrariaceae, Peganaceae.

Habit and leaf form. Trees, or shrubs (mostly, sometimes with short-shoots), or herbs (often with jointed nodes); resinous, or not resinous. ‘Normal’ plants, or switch-plants (sometimes, more or less); sometimes more or less phyllodineous (e.g., species in which the leaflets fall before the photosynthesising petioles). Plants succulent, or non-succulent. The herbs perennial (mostly), or annual (some species of Kallstroemia, Tribulus and Zygophyllum). Xerophytic (and often halophytic, in salt-deserts). Leaves opposite (usually), or alternate (e.g. Viscainoa); when alternate, spiral; ‘herbaceous’, or leathery, or fleshy, or modified into spines; petiolate (mostly), or sessile (e.g. Augea); non-sheathing; compound (nearly always), or simple (supposedly, e.g. in some Zygophyllum and Fagonia species); pulvinate, or epulvinate; usually unifoliolate, or bifoliolate, or ternate, or pinnate; when pinnate, paripinnate. Leaflets pulvinate, or epulvinate. Lamina one-veined, or pinnately veined; cross-venulate (small veins often terminating in dilated tracheids). Leaves stipulate. Stipules free of one another; spiny (often), or scaly, or leafy; persistent. Leaf development not ‘graminaceous’.

Leaf anatomy. The leaf lamina dorsiventral (usually), or bifacial, or centric. Mucilaginous epidermis present, or absent. Stomata mainly confined to one surface, or on both surfaces; anomocytic (mostly), or paracytic, or actinocytic. Hairs present, or absent (Augea); eglandular, or glandular; when present, unicellular (mostly), or multicellular. Unicellular hairs branched (rarely, two-armed), or simple (mostly). Multicellular hairs branched, or simple. Complex hairs present, or absent; when present, capitate. Adaxial hypodermis present, or absent. The mesophyll containing mucilage cells (e.g., in Nitraria spp.), or not containing mucilage cells; with sclerenchymatous idioblasts (and then these also common in stems), or without sclerenchymatous idioblasts; containing crystals. The crystals druses, or solitary-prismatic, or raphides (rarely). Minor leaf veins without phloem transfer cells (Tribulus, Zygophyllum).

Axial (stem, wood) anatomy. Young stems with solid internodes (mostly), or with hollow internodes (in Zygophyllum fabago). Pith homogeneous (usually, consisting of thin-walled cells), or heterogeneous (sometimes containing stone cells). Secretory cavities absent. Cork cambium present; initially deep-seated, or initially superficial (usually). Nodes tri-lacunar (with the lateral gaps associated with a split trace and very closely opposed); commonly exhibiting on either side a trace which divides, contributing the outermost lateral traces to each of the opposite leaves (exemplified in five genera), or without split-lateral traces (?). Primary vascular tissues in a cylinder, without separate bundles, or comprising a ring of bundles (then comprising closely placed bundles). Internal phloem absent. Secondary thickening developing from a conventional cambial ring, or anomalous. Primary medullary rays narrow.

The wood semi-ring porous (rarely), or diffuse porous. The vessels small (to very small, usually), or medium (Balanites and Guaiacum); solitary, or radially paired to in radial multiples, or clustered (notably so in Balanites). The vessel end-walls horizontal to oblique; simple. The vessels without vestured pits; without spiral thickening. The axial xylem with tracheids, or without tracheids (?); often with vasicentric tracheids; with fibre tracheids, or without fibre tracheids; with libriform fibres, or without libriform fibres; without septate fibres. The fibres without spiral thickening. The parenchyma usually typically apotracheal (diffuse or in uniseriate bands), or paratracheal (Bulnesia). The secondary phloem not stratified. ‘Included’ phloem absent. The wood storied (in most genera).

Reproductive type, pollination. Unisexual flowers present, or absent. Plants hermaphrodite (mostly), or dioecious (Neoluederitzia). Pollination entomophilous.

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; when solitary, terminal, or axillary (or leaf-opposed). The ultimate inflorescence units when flowers aggregated, cymose. Inflorescences terminal, or axillary, or leaf-opposed. Flowers ebracteate; ebracteolate; regular; not resupinate; (4–)5(–6) merous; cyclic; tetracyclic, or pentacyclic, or polycyclic. Floral receptacle developing a gynophore, or with neither androphore nor gynophore. Free hypanthium absent. Hypogynous disk present (usually), or absent (sometimes with nectariferous glands between the perianth whorls as well as or instead of those between stamens and ovary); when present, extrastaminal (usually), or intrastaminal; of separate members, or annular.

Perianth with distinct calyx and corolla (usually), or sepaline (the corolla sometimes lacking, e.g. Seetzenia); (4–)5, or (8–)10(–12); (1–)2 whorled; isomerous. Calyx (4–)5(–6); 1 whorled; polysepalous, or gamosepalous; regular; imbricate (usually), or valvate. Corolla when present, (4–)5(–6); 1 whorled; polypetalous; imbricate, or contorted, or valvate (rarely); regular; white, or yellow, or red, or blue (rarely).

Androecium (4–)5, or 10, or 15. Androecial members free of the perianth; free of one another; 1–3 whorled. Androecium exclusively of fertile stamens, or including staminodes (e.g. in Tribulus, where the antesepalous whorl may be sterile). Staminodes when present, 4, or 5; external to the fertile stamens. Stamens (4–)5, or 10, or 15; isomerous with the perianth, or diplostemonous, or triplostemonous; alternisepalous, or oppositisepalous (when the outer whorl is staminodal); alternating with the corolla members, or both alternating with and opposite the corolla members. Filaments appendiculate (commonly, with basal ligular scales which may unite to form an appendage within the staminal ring), or not appendiculate. Anthers dorsifixed; versatile; dehiscing via longitudinal slits; introrse, or latrorse; tetrasporangiate. Endothecium developing fibrous thickenings. Anther epidermis persistent. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral, or isobilateral, or decussate. Anther wall initially with one middle layer, or initially with more than one middle layer (up to 3); of the ‘dicot’ type. Tapetum glandular. Pollen grains aperturate; 3 aperturate, or 4–20 aperturate (to ‘polyforate’); colpate, or porate, or colporate, or foraminate, or rugate; 2-celled (in 4 genera), or 3-celled (Tribulus only).

Gynoecium (2–)5(–6) carpelled. Carpels isomerous with the perianth (usually), or reduced in number relative to the perianth, or increased in number relative to the perianth. The pistil (2–)4–12 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary (2–)5(–6) locular (but sometimes these secondarily partitioned). Locules secondarily divided by ‘false septa’ (in Tribulus), or without ‘false septa’. Ovary sessile, or subsessile, or stipitate (in several New World genera). Gynoecium non-stylate, or stylate. Styles 1; attenuate from the ovary; apical. Stigmas 1; lobed or capitate; wet type, or dry type; papillate; Group II type, or Group III type. Placentation axile. Ovules 1–50 per locule (to ‘several’ or to ‘many’); pendulous; apotropous; with ventral raphe; non-arillate; anatropous (usually), or hemianatropous, or orthotropous, or campylotropous; bitegmic; crassinucellate. Outer integument contributing to the micropyle, or not contributing to the micropyle. Endothelium differentiated, or not differentiated. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral (usually), or persistent. Synergids pear-shaped. Endosperm formation nuclear. Embryogeny solanad.

Fruit non-fleshy (usually), or fleshy; dehiscent (usually), or indehiscent, or a schizocarp. Mericarps when schizocarpic, 2–5; these indehiscent ‘cocci’, often angular, winged or spiny. Fruit when non-schizocarpic, a capsule (usually), or capsular-indehiscent. Capsules septicidal, or loculicidal, or septicidal and loculicidal. Fruit elastically dehiscent (when of cocci), or passively dehiscent. Seeds endospermic, or non-endospermic. Endosperm oily. Cotyledons 2. Embryo chlorophyllous (3/3); straight, or curved.

Seedling. Germination phanerocotylar, or cryptocotylar.

Physiology, phytochemistry. C3, or C4. C3 physiology recorded directly in Bulnesia, Fagonia, Guaiacum, Kallstroemia, Larrya, Neoluederitzia, Porlieria, Seetzenia, Sisyndite, Viscainoa, Zygophyllum. C4 physiology recorded directly in Kallstroemia, Tribulus, Zygophyllum. Anatomy C4 type (Tribulus, Zygophyllum: see illustration), or non-C4 type (Zygophyllum). Sugars transported as sucrose (in Bulnesia). Mustard-oils present. Not cyanogenic. Alkaloids present (commonly), or absent. Iridoids not detected. Saponins/sapogenins present (commonly), or absent. Proanthocyanidins absent. Flavonols present; kaempferol and quercetin. Ellagic acid absent (Zygophyllum). Aluminium accumulation not found.

Geography, cytology. Temperate to tropical. Widespread tropical, subtropical and warm temperate, often in drier areas. X = 6, 8–13(+).

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Corniflorae; Cornales. Cronquist’s Subclass Rosidae; Sapindales. APG III core angiosperms; core eudicot; Superorder Rosanae; fabid. APG IV Order Zygophyllales.

Species 235. Genera about 30; Augea, Bulnesia, Fagonia, Guaiacum, Halimiphyllum, Izozogia, Kallstroemia, Kelleronia, Larrea, Metharme, Miltianthus, Morkillia, Neoluederitzia, Pintoa, Plectrocarpa, Porlieria, Roepera, Sarcozygium, Seetzenia, Sericodes, Sisyndite, Tetradiclis (APG Nitrariaceae), Tetraena, Tribulopis, Tribulus, Viscainoa, Zygophyllum.

General remarks. Analyses of rbcL sequence and other data (see Sheahan and Chase 1996) resulted in removal of the truly sapindalean Nitraria (Nitrariaceae) and Peganum and Malacocarpus (Peganaceae), but left the affinities of Zygophyllaceae s. str. in doubt. The rbcL sequence data (see also Chase et al. 1993, Gadek et al 1996) linked Zygophyllaceae loosely with Krameria and the Polygalales, associating them with Rosiflorae rather than Rutiflorae. Some of the above variation attributed here to characters ignored by Sheahan and Chase (e.g., in anther development, embryology and pollen structure) may now be spurious ........

Economic uses, etc. Guaiacum officinale is the source of the hardest, densest wood (lignum vitae); Guaiacum, Zygophyllum, Tribulus and Larrea species are cultivated in warm regions as ornamentals; and this family is said to include the few plants poisonous to camels.

Illustrations. • Fagonia arabica: Kirtikar & Basu, Indian Medicinal Plants 1 (1918). • Guaiacum officinale: Köhler’s Medizinal-Pflanzen 2 (1890). • Guaiacum officinale: Bot. Reg. 9 (1839). • Kallstroemia maxima: Fawcett & Rendle, Flora of Jamaica 4 (1920). • cf. Kallstroemia tribuloides, as Ehrenbergia: Martius, Nova Gen. et Spec. Pl. Brasiliensium 2 (1826). • Tetraena alba, as Zygophyllum amblyocarpum: Hook. Ic. Pl. 24 (1895). • Tribulus cistoides: Fawcett & Rendle, Flora of Jamaica 4 (1920). • Le Maout and Decaisne: Tribulus terrestris. • Le Maout and Decaisne: Zygophyllum, Seetzenia. • Zygophyllum insuave: Bot. Mag. 372 (1797). • Zygophyllum foetidum: Bot. Mag. 372 (1797), text. • Leaf hairs of Fagonia and Larrea, and leaf TS of Tribulus alatus: Solereder, 1908.

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: 8th June 2026. delta-intkey.com’.

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