Ebonwood

Ebonwood is a type of extremely hard, dark wood harvested from the massive trees of the Techeryan Jungle. In addition to being incredibly strong, it possesses the unique ability to continue growing even after its refinement into lumber.
Ebonwood has long been known for being extremely light while also incredibly hard, and therefore was long hoped to be used for shipbuilding. However its most unique property, that of continuing to grow after harvesting, proved this impossible; the few ships built from ebonwood became a gnarled mass of wood within a matter of weeks. It was not until the discovery of a special type of sealant previously known only to the grung natives of the Techeryan jungle that the use of ebonwood became practical. When this sealant was applied to a structure made of ebonwood it not only prevented further growing, but it also caused the wood to "remember" its shape and re-grow back in place if damage was sustained to it—in essence forming a self-healing building material.
The exact composition of this sealant is a closely-guarded secret of the Keshites, and has allowed them to leverage its abilities to create a small fleet of extremely fast, durable, and self-healing ships.