( Guaiacum  ), sometimes spelled  , is a Guajacum genus of flowering plants in the caltrop family Zygophyllaceae. It contains five species of slow-growing shrubs and trees, reaching a height of approximately 20 m (66 ft) but usually less than half of that. All are native to subtropical and tropical regions of the Americas and are commonly known as lignum-vitae, guayacán ( Spanish), or gaïac ( French). The genus name originated in  Maipurean, the language spoken by the native Taínos of the Bahamas; it was adopted into English in 1533, the first word in that language of American origin. 
Members of the genus have a variety of uses, including as
lumber, for medicinal purposes, and as ornamentals. The trade of all species of Guaiacum is controlled under CITES Appendix II. 
is the Guaiacum officinale national flower of Jamaica, while  is the Guaiacum sanctum national tree of the Bahamas. 
The genus is famous as the supplier of
lignum vitae, which is the heartwood of several species in the genus. It is the fourth-hardest variety of wood as measured by the Janka hardness test, requiring a force of 4,500 lb f (20,000 N) to embed a steel ball 0.444 in (1.13 cm) in diameter half that distance into the wood. 
The Spanish encountered guaiacum wood when they conquered
San Domingo in the sixteenth century. It was soon brought back to Europe, where epidemic syphilis had been raging for nearly a century. Gum guiacum quickly acquired a reputation as a cure for syphilis, a practice  Benvenuto Cellini records in his memoirs.  Thomas Nashe referred to its supposed medical properties in his tract Nashe's Lenten Stuff, alluding to the exotic sound of the word itself: "Physicians deafen our ears with the of their heavenly honorificabilitudinitatibus panacaea, their sovereign guiacum." The detailed engraving,  Preparation and Use of Guayaco for Treating Syphilis, published by Philips Galle after a design by the Flemish artist Jan van der Straet, depicts four servants preparing a concoction of gum guiacum for their wealthy master under the supervision of a physician.  Paracelsus, the famous if controversial Swiss physician, disputed the effectiveness of this treatment and was censured for his criticism.
Gum guaicum was used to stimulate
menstruation; in a 1793 Virginia court case, Martha Jefferson Randolph testified that she had provided gum guaiacum to a female relative to "produce an abortion", suggesting that it was also used as an  abortifacient. In A Treatise of the Materia Medica (1789), Scottish physician William Cullen noted: "Several physicians have apprehended mischief from the use of the guaiacum in a spirituous tincture."  
The 1955 edition of the
"Guaiacum has a local Textbook of Pharmacognosy stimulant action which is sometimes useful in sore throat. The resin is used in chronic gout and rheumatism, whilst the wood is an ingredient in the compound concentrated solution of sarsaparilla, which was formerly much used as an alternative in syphilis." 
phenolic compound derived from the resin of Guaiacum trees is used in a common test for blood in human stool samples. The presence of heme in the blood causes the formation of a coloured product in the presence of hydrogen peroxide. The effect of peroxidases in horseradish on guiacum was first noted in 1810. 
food additive, Guaiacum is designated E314 and classified as an antioxidant.
A widely used derivative drug is the
expectorant known as guaifenesin.
fragrance oil of guaiac comes from , a Bulnesia sarmientoi South American tree from the same family.
Members of the genus are grown in
Florida and California as ornamental plants.
Formerly placed here
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