Analysis of osage orange (Maclura pomifera) heartwood extractives show
ed that two compounds were present at much higher levels than previous
ly reported, the flavanonol dihydromorin (2.51%) and the stilbene oxyr
esverauol (2.65%). All compounds present in osage orange heartwood tha
t were tested bad low activity against wood-decaying fungi. The agar p
late test showed no synergistic effect, but the soil block test using
white-rot fungi suggested synergism. The high durability of osage oran
ge heartwood may be due to the large amounts of oxyresveratrol and dih
ydromorin. High levels of one or two monomeric compounds may also expl
ain the exceptionally good durability of black locust and red mulberry
heartwood.