Zygophyllaceae

Herbs, subshrubs, shrubs, or trees, annual or perennial, branching usually divaricate, growth sympodial, nodes angled or swollen, evergreen [deciduous], synoecious [dioecious]. Leaves opposite or fascicled [alternate or on short lateral branches], palmately or even- [odd-]pinnately compound [simple]; stipules present; petiole present [absent]; blade often fleshy or coriaceous, margins entire; venation pinnate. Inflorescences pseudoaxillary [terminal], flowers solitary or in 2-flowered clusters [cymes]. Flowers bisexual [unisexual], usually regular, sometimes slightly irregular; perianth and androecium hypogynous; hypanthium absent; sepals 4–5, usually distinct, rarely connate basally; petals 4–5, distinct [rarely connate basally], often clawed, sometimes twisted; nectary usually present, extrastaminal and/or intrastaminal, rarely absent; stamens [5–](8–)10 in 2 whorls, outer usually opposite petals, often alternately unequal in length or sterile, distinct, free or adnate to petal bases, inserted on or proximal to nectary, frequently glandular or appendaged at base; anthers dehiscing by longitudinal slits; pistil 1, (2–)5-carpellate, ovary superior, (2–)5–10-locular; placentation axile [basal]; ovules (1–)2–10 per locule, anatropous; style 1; stigma 1. Fruits capsules, dehiscence septicidal or loculicidal, or schizocarps splitting into 5 or 10 mericarps. Seeds 1–5(–10) per locule.

Distribution

North America, Mexico, West Indies, Central America, South America, Eurasia, Africa, Atlantic Islands, Indian Ocean Islands, Pacific Islands, Australia, mostly tropical or subtropical regions, mainly in arid and semiarid areas.

Discussion

Genera 27, species ca. 240 (6 genera, 15 species in the flora).

Zygophyllaceae are most closely related to Krameriaceae and the two families make up the isolated order Zygophyllales (Angiosperm Phylogeny Group 2003). A number grow in saline soils. Three species are cultivated in milder winter areas of the southeastern United States for their colorful flowers: the South American Bulnesia arborea (Jacquin) Engler and B. sarmientoi Lorentz ex Grisebach, both verawood, and the Caribbean Guaiacum officinale Linnaeus, lignum vitae. Guaiacum coulteri A. Gray, guayacán, from western Mexico and Guatemala, is grown in southern Arizona. Peganum, often placed in the Zygophyllaceae, is now recognized to be a member of the unrelated Nitrariaceae (Angiosperm Phylogeny Group).

Selected References

Beier, B.-A. et al. 2004. Phylogeny and taxonomy of the subfamily Zygophylloideae (Zygophyllaceae) based on molecular and morphological data. Pl. Syst. Evol. 240: 11–40.

Porter, D. M. 1972. The genera of Zygophyllaceae in the southeastern United States. J. Arnold Arbor. 53: 531–552.

Porter, D. M. 1974b. Disjunct distributions in the New World Zygophyllaceae. Taxon 23: 339–346.

Sheahan, M. C. and M. W. Chase. 1996. A phylogenetic analysis of Zygophyllaceae R. Br. based on morphological, anatomical and rbcL DNA sequence data. Bot. J. Linn. Soc. 122: 279–300.

Sheahan, M. C. and M. W. Chase. 2000. Phylogenetic relationships within Zygophyllaceae based on DNA sequences of three plastid regions, with special emphasis on Zygophylloideae. Syst. Bot. 25: 371–384.

Lower Taxa

Fagonia, Guaiacum, Kallstroemia, Larrea, Tribulus, Zygophyllum

Illustrations

	Family ⠉	Plate of taxon	Illustrator ⠉
	Zygophyllaceae Zygophyllaceae Zygophyllaceae Zygophyllaceae	Fagonia longipes Fagonia laevis Zygophyllum fabago Larrea tridentata	Barbara Alongi Barbara Alongi Barbara Alongi Barbara Alongi
	Zygophyllaceae Zygophyllaceae Zygophyllaceae Zygophyllaceae	Kallstroemia parviflora Tribulus terrestris Tribulus cistoides Guaiacum angustifolium	Barbara Alongi Barbara Alongi Barbara Alongi Barbara Alongi

Key

1	Leaflets 2.	> 2
2	Leaflets distinct.	Zygophyllum
2	Leaflets connate basally, leaves appearing simple and 2-lobed.	Larrea
1	Leaflets (1–)3 or (4–)6–16(–20).	> 3
3	Leaves palmately compound; leaflets (1–)3, apex spinose or spinulose.	Fagonia
3	Leaves pinnately compound; leaflets (4–)6–16(–20), apex not spinose.	> 4
4	Trees or shrubs; petals usually blue to purple, rarely white; fruits capsules, 2–5-lobed.	Guaiacum
4	Herbs; petals white or yellow to bright orange, bases sometimes green or red; fruits schizocarps, 5-angled or 10-lobed.	> 5
5	Ovaries 5-lobed, 5-locular; fruits 5-angled, spiny, breaking into 5 mericarps (rarely fewer); petals yellow, base darker; nectary 10 glands in 2 whorls.	Tribulus
5	Ovaries 10-lobed, 10-locular; fruits 10-lobed, not spiny, breaking into 10 mericarps (sometimes fewer); petals white to bright orange, base white to bright orange or green to red; nectary 5 glands at bases of filaments opposite petals.	Kallstroemia