AusBonsai

a ligno tuber is the big bulbous base you see on olives and eucs and some other trees. it is full of stored water and energy mate

Here's a tuber. It is the big solid bit at the bottom. Full of stored energy, which is exactly why we cut it off!!!! (not all of it mind you!)

lignotuber - swollen base of a woody plant. Trunks grow from the top, roots from the lower section. Lignotubers appear to store energy to allow the plant to survive catastrophes. Many plants from bushfire prone areas have lignotubers. After a fire kills the trunks, new ones sprout from the lignotuber - mallee eucalypts, snowgums. Some trees from dry areas also use lignotubers to survive - a really bad drought will kill the trunks but the energy in the lignotuber allows the tree to resprout when conditions improve.
You will note that trees that sprout from lignotubers frequently have multitrunk form eg mallee eucs, snowgum, olive and irish strawberry are a few that come to mind.