Lignum vitae is the heartwood of species of the genus Guaiacum, the trees of which are also called guayacan. The name is Latin for "wood of life", and derives from its medicinal uses. Other names are palo santo, holy wood, greenheart and ironwood (one of many). The wood is obtained chiefly from Guaiacum officinale and Guaiacum sanctum, both small, slow growing trees.
Bulnesia Sarmientoi, known commercially as Argentine Lignum Vitae, is not genetically related to genuine lignum vitae. Bulnesia Sarmientoi is related to, but not the same as Bulnesia Arborea, known commercially as Verawood.
This wood has a density between 1.28 and 1.37g per cu.cm., so it will sink in water. It is a hard, dense and durable wood, the most dense of any known wood. The wood was important for uses requiring strength, weight and hardness. On the Janka Scale of Hardness, which measures the relative density of various types of wood, lignum vitae ranks highest, with a Janka hardness of 4500 (compared with Hickory at 1820, red oak at 1290, and Yellow Pine at 690). The heartwood is green in color leading to the common name Greenheart. In the shipbuilding, cabinetry, and woodturning crafts the term greenheart refers to the green heartwood of the Chlorocardium genus trees.
Verawood (Bulnesia sarmientoi/arborea) is an unrelated species also known as Argentine lignum vitae due to similar appearance and working qualities to lignum vitae. It has a strong, fresh aroma and is used as incense.
Master clockmaker John Harrison used lignum vitae as the basis for his nearly all-wood clocks, since the wood provides natural lubricating oils which do not dry out. For this reason it was widely used in shaft bearings. According to the San Francisco Maritime National Park Association website, the shaft bearings on the WWII submarine USS Pampanito (SS-383) were made of this wood. (Source:http://www.maritime.org/pamphist.htm) The after main shaft strut bearings for USS Nautilus SSN571; the worlds first nuclear powered submarine were composed of this wood. Also, the bearings in the original 1920's turbines of the Conowingo Hydroelectric Plant on the lower Susquehanna River were made from lignum vitae.
It was the traditional wood used for British police truncheons until recently, due to its density (and strength), combined with the relative softness of wood compared to metal, thereby tending to bruise or stun rather than simply cut the skin.