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. Perennial. 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. 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. Leaves without a persistent basal meristem.
Leaf anatomy. 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, or multicellular. Unicellular hairs branched, or unbranched. Multicellular hairs branched, or unbranched. Complex hairs present, or absent; when present, capitate.
Adaxial hypodermis present, or absent. Lamina dorsiventral (usually), or centric. The mesophyll not containing mucilage cells; with sclerencymatous idioblasts (and these common in stems), or without sclerenchymatous idioblasts. Minor leaf veins without phloem transfer cells (Tribulus, Zygophyllum).
Stem anatomy. Secretory cavities absent. Cork cambium present; initially deep-seated, or superficial (usually). Nodes tri-lacunar. Primary vascular tissue in a cylinder, without separate bundles. Internal phloem absent. Secondary thickening developing from a conventional cambial ring, or anomalous. ‘Included’ phloem absent. Xylem with fibre tracheids, or without fibre tracheids; with libriform fibres, or without libriform fibres; with vessels. Vessel end-walls horizontal to oblique; simple. Vessels without vestured pits. Primary medullary rays narrow. Wood storied (most genera); parenchyma usually typically apotracheal (diffuse or in uniseriate bands), or paratracheal (Bulnesia).
Reproductive type, pollination. Plants hermaphrodite (mostly), or dioecious (Neoluederitzia). Entomophilous.
Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; when solitary, terminal, or axillary (or leaf-opposed). The terminal inflorescence unit when flowers aggregated, cymose. Inflorescences terminal, or axillary, or leaf-opposed; espatheate. 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); 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 unbranched; 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, or 3-celled.
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; 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. Perisperm absent. Cotyledons 2. Embryo chlorophyllous (3/3); straight, or curved. Micropyle not zigzag.
Seedling. Germination phanerocotylar, or cryptocotylar.
Physiology, biochemistry. Mustard-oils present. Not cyanogenic. Alkaloids present (commonly), or absent. Iridoids not detected. Proanthocyanidins absent. Flavonols present; kaempferol and quercetin. Ellagic acid absent (Zygophyllum). Saponins/sapogenins present (commonly), or absent. Aluminium accumulation not found. Sugars transported as sucrose (in Bulnesia). C3 and C4. C3 physiology recorded directly in Bulnesia, Fagonia, Guaiacum, Kallstmemia, Larrya, Neoluederitzia, Porlieria, Seetzenia, Sisyndite, Viscainoa, Zygophyllum. C4 physiology recorded directly in Kallstroemia, Tribulus, Zygophyllum. Anatomy C4 type (Tribulus, Zygophyllum), or non-C4 type (Zygophyllum).
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 Rutiflorae; Geraniales. Cronquist’s Subclass Rosidae; Sapindales. APG (1998) Eudicot; core Eudicot; Rosid; unassigned to Eurosid I or Eurosid II; unassigned to order. Species 235. Genera about 30; Augea, Bulnesia, Fagonia, Guaiacum, Halimiphyllum, Izozogia, Kallstroemia, Kelleronia, Larrea, Metharme, Miltianthus, Morkillia, Neoluederitzia, Peganum, Pintoa, Plectrocarpa, Porlieria, Roepera, Sarcozygium, Seetzenia, Sericodes, Sisyndite, Tetradiclis, Tetraena, Tribulopis, Tribulus, Viscainoa, Zygophyllum.
Recent analyses of rbcL sequence and other data (see Sheahan and Chase 1996) result in removal of the truly sapindalean Nitraria (Nitrariaceae) and Peganum and Malacocarpus (Peganaceae), but leave the affinities of Zygophyllaceae s. str. in doubt. The rbcL sequence data (see also Chase et al. 1993, Gadek et al 1996) link 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.
Illustrations. • Technical details (Zygophyllum, Tribulus, Seetzenia). • Technical details (Tribulus).
Cite this publication as: ‘L. Watson and M. J. Dallwitz (1992 onwards). The Families of Flowering Plants: Descriptions, Illustrations, Identification, and Information Retrieval. Version: 14th December 2000. http://biodiversity.uno.edu/delta/’. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993, 1995, 2000), and Watson and Dallwitz (1991) should also be cited (see References).
