Dark and woody fragrance
In order for us to obtain this rich and fragrant ingredient we have to rely on a certain tropical tree, (the agar tree), being infected by a certain type of mould (Phialophora parasitica seeing as you asked!) The infected tree reacts by producing the precious and rare resin called oudh.
It’s not even that simple, as not all agarwood trees get affected by the mould and not all trees affected actually produce the growth. This complicated process means it is all very random and that oudh is extremely rare.
Due to all these factors oudh is one of the most expensive oils in the world costing more than gold by weight. The dark and woody base note tones it provides are worth all the trouble and expense.