Including Nitrariaceae Lindl., Peganaceae Van Tiegh., Tribulaceae Trautv.
Habit and leaf form. Trees, or shrubs (mostly), or herbs (often with jointed nodes); resinous, or not resinous. Plants succulent, or non-succulent. Perennial. Xerophytic (and often halophytic, in salt-deserts). Leaves opposite (usually), or alternate; when alternate, spiral; `herbaceous', or leathery, or fleshy, or modified into spines; non-sheathing; not gland-dotted; compound; unifoliolate, or bifoliolate, or ternate, or pinnate. Lamina pinnately veined; cross-venulate. Leaves stipulate. Stipules free of one another; often spiny; persistent. Leaves without a persistent basal meristem.
Leaf anatomy. Stomata mainly confined to one surface, or on both surfaces; anomocytic.
Adaxial hypodermis present, or absent. Lamina dorsiventral (usually), or centric. The mesophyll containing mucilage cells (Nitraria), or not containing mucilage cells. Minor leaf veins without phloem transfer cells (Tribulus, Zygophyllum).
Stem anatomy. Cork cambium present; initially deep-seated, or superficial (usually). Nodes tri-lacunar. Internal phloem absent. Secondary thickening developing from a conventional cambial ring, or anomalous. `Included' phloem absent. Xylem with fibre tracheids; with vessels. Vessel end-walls simple. Vessels without vestured pits. Wood storied (most genera); parenchyma usually typically apotracheal (diffuse or in uniseriate bands), or paratracheal (Bulnesia, Nitraria).
Reproductive type, pollination. Hermaphrodite. Entomophilous.
Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in `inflorescences'. The terminal inflorescence unit 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; extrastaminal (usually), or intrastaminal.
Perianth with distinct calyx and corolla (usually), or sepaline (the corolla sometimes lacking); (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. Stamens (4-)5, or 10, or 15; isomerous with the perianth, or diplostemonous, or triplostemonous; alternisepalous, or oppositisepalous (when the outer whorl is staminodal). 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). Carpels isomerous with the perianth (usually), or reduced in number relative to the perianth, or increased in number relative to the perianth. Gynoecium syncarpous; eu-syncarpous; superior. Ovary (2-)5(-6) locular, or 4-12 locular (via secondary septa, in Tribulus). 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; 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; when schizocarpic, comprising mericarps (`indehiscent cocci'); when non-schizocarpic a capsule (usually), or a berry, or a drupe. 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, biochemistry. Mustard-oils present. Not cyanogenic. Alkaloids present (commonly), or absent. Iridoids absent. Proanthocyanidins absent. Flavonols present; kaempferol and quercetin. Ellagic acid absent (Zygophyllum). Saponins/sapogenins present (commonly), or absent. Aluminium accumulation not found. C3 and C4. C3 recorded in Fagonia, Larrya, Nitraria, Peganum, Seetzenia, Zygophyllum. C4 recorded in Kallstroemia, Tribulus, Zygophyllum. Anatomy C4 type (Tribulus, Zygophyllum), or non-C4 type (Nitraria, Peganum, 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. Takhtajan's Subclass Rosidae; Rutanae; Rutales. Species 240. Genera about 30; Augea, Bulnesia, Fagonia, Guaiacum, Halimiphyllum, Kallstroemia, Kelleronia, Larrea, Malocarpus, Metharme, Miltianthus, Morkillia, Neoluederitzia, Nitraria, Peganum, Pintoa, Plectrocarpa, Porlieria, Roepera, Sarcozygium, Seetzenia, Sericodes, Sisyndite, Tetradiclis, Tetraena, Tribulopis, Tribulus, Viscainoa, Zygophyllum.
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. zygop303.gif zygop304.gif
Additional, to be intercalated. Flowers when solitary, terminal, or axillary (or leaf-opposed).
