Zygophyllaceae  

Leaves opposite or sometimes alternate, usuallypinnate, rarely 3-foliolate or 2-foliolate or simpleand entire, leathery, fleshy, or modified intospines, usually with stipules (sometimes spiny, or scaly, or leafy, persistent). Stomata mostly anomocytic. Small trees or shrubs, rarely perennial or annual herbs, resinous or not resinous, more or less succulent. Wood often fluorescing; vessels with simple perforation and usually with vestured pits. Axial parenchyma diffuse or diffuse-in-aggregates; rays heterogenerous or homogeneous; crystals one per cell or septate portion of cell in wood or secondary phloem (Carlquist 2005). Nodes often swollen  or jointed. Flowers in cymose inflorescences or solitary, terminal or axillary, or leaf-opposed, bisexual or very rarely unisexual and dioecious (Neoluederitzia), actinomorphic, 5-merous or sometimes 4-merous. Sepals free or less often basally connate,imbricate or valvate.Petals usually free,imbricate or contorted, rarely valvate, sometimes wanting (Seetzenia). Nectary discusually present, extrastaminal or intrastaminal. Stamens in (1)2(3) cycles, alternisepalous, oroppositisepalous, when the outer whorld is staminodal; filaments often with basal ligular appendages; anthers versatile, introrse, or latrorse.

Pollen grains mostly 3-colporate, less often 3-colpate (Seetzenia,) or pantoporate (Tribuloideae). Gynoecium of five or less often four carpels, gradually attenuated into a simple style with lobed or capitate stigma; ovary often angled or winged, 5–6-locular (in Tribulus locules secondarily divided by ‘false septa’), with one to many axile, pendulous, apotropous to orthotropous or campylotropous ovules per locule; micropyle not zig-zag. Endothelium present (absent in Seetzenia). Fruits usually loculicidal and/or septicidal capsules or schizocarps. Fruit elastically dehiscent (when of cocci), or passively dehiscent. Seeds with straight to weakly curved, green embryo, with oily or without endosperm; seed-coat with endotestal crystal layer and a lignified endotemgen. Present anthroquinones, flavonols (kaempferol and quercetin), some species produce steroid and triterpenoid saponins, alkaloids (harman, harmin, and harmol); n = 6, 8–13 or (Tetraena).

1.1 ZYGOPHYLLOIDEAE

Shrubs, herbs, or rarely trees. Leaves alternate (Sericodes and Plectrocarpa) or more often opposite, paripinnate or imparipinnate, often 2-foliolate, sometimes unifoliolate or simple, stipulate. Nectary discusually present, often small. Pollen grains 3-colporate or rarely (Seetzenia) 3-colpate. Gynoecium of 5–2carpels. Fruits capsular, dehiscing septicidally or breaking into cocci. Seeds usually with endosperm. –seetzenieae: Seetzenia; sisynditeae: Sisyndite; sericodeae: Sericodes; zygophylleae: Zygophyllum, Fagonia; larreae: Guaiacum; morkillieae: Viscalnoa.

1.2. TETRAENOIDEAE
Shrubs with very tortuous branches and short, lateral branchlets. Young shoots and leaves covered by 2-armed trichomes. Axial parenchyma scanty metatracheal and vasicentric. Leaves alternate, 2- foliolate. Flowers solitary in the leaf axils, 4-merouswith a very short androgynophore. Sepals imbricate. Petals valvate. Stipules membranous, lacerate.
Stamens eight in two cycles; filaments with membranous scaly appendage at the base. Pollen grains 3-colporate. Nectary disc annular. Gynoecium of 4-carpels with long, simple, persistent style and capitate stigma; ovary deeply lobed, with 3–5 ovules per locule; ovules orthotropous, with long, curved funicles. Fruits deeply 4-lobed, breaking into four one seeded indehiscent cocci, with the style in the middle, indehiscent; exocarp spongy, densely villose. Seeds one in each locule, oblong, with thick testa; embryo oblong-ovoid, green, with fleshy cotyledons; endosperm wanting, n = 14. – Tetraena.

1.3 TRIBULOIDEAE
Shrubs (Kelleronia) or biennial prostrate herbs. Leaves alternate or opposite, pinnate, stipulate. Trichomes of two markedly different sizes: short and pointed, or much longer and wider. Pollen grains pantocolpa1.2te. Nectary disc present, lobed. Fruits breaking up into five cocci (Kelleronia), dividing by oblique transverse septa into 5–3 one-seeded compartments (Tribulus) or separating into 12–5 indehiscent 1- or rarely 2-seeded cocci. Seeds without endosperm. – Tribulus.