For wooden swords wood from trees such as the bamboo-leaved oak, the Japanese evergreen oak, and the distylium racemosum have been used. For top quality swords, the Japanese plum tree, ebony, and sunuke have been used. Sunuke refers to the core wood taken from distylium racemosum (isunoki) that has grown for more than 200 years. The old wood has worn away and only the core is used. It is also called isunuke. It has a distinct dark reddish-brown color and the wood is heavy and tough and is of top quality in terms of weight, strength, luster and sound.
From old times, sunuke was valued as material for combs, for traditional ornaments, and for shamisen (a native Japanese instrument) which requires dense wood because of the tuning. Among the samurai, sunuke combs were preferred over the more generally used boxwood combs. Most of the boxwood came from an island called Hachijojima, but that was also the island where convicts were sent to. Some speculate that for this reason the samurai used sunuke combs instead. The quality of wood and its color makes it top material for ornamental combs. Because the sunuke is taken from isunoki trees that have survived a tough natural environment, the material is believed to have good omens of longevity and warding off sicknesses and evil spirits.
The fiber is also very tough, just like the ebony wood and polishing the wood gives it a nice luster which makes it fir for high quality alcove posts, tokogamachi (an ornamental wooden bar in front of the alcove), and the lintels.
The Jigen-ryu swordsmen used for their swords the isunoki before it was turned into sunuke. Its strength is greater than the bamboo-leaved oak or the evergreen oak and it is among the heaviest and strongest wood from any Japanese tree. But since it is an old tree the fiber no longer sticks to each other, so it would often crack along the fiber lines.
Recently we do not see much of sunuke anymore, and it is becoming increasingly rare. If you compare a wooden sword made from sunuke 20 years ago to one made from sunuke recently, the strength and weight are the same but the more recent ones have lost the strong color. Within the next few years, sunuke is still purchasable but because of its rarity the price is likely to keep increasing. If you are looking for a special wooden sword, it may be good to buy a sunuke sword now.