Lignum Vitae IS Ironwood.
Not necessarily. Ironwood is used to describe quite a number of very hard woods, not all of which would be suitable. Sometimes another term is used to specify what is meant (e.g., "desert ironwood") but not always, so the name ironwood won't tell you what it is. For example, when someone says ironwood to me, I think of the stuff that grows in the Arizona desert, a very different thing than lignum vitae. At least in the western U.S., if you see "ironwood" for sale, it is likely that it is the desert stuff, not what you want.
Where I live now in Indiana some folks refer to osage orange/hedge apple as ironwood (although it usually just gets called "hedge"). It, at least, might work in place of lignum vitae: similar hardness (nails spark when driven into it) and similarly high oil content.
-Arle
