Eucalyptus spp. of the family Myrtaceae. Native to Australia. Also sometimes spelled morrell. Includes at least Eucalyptus longicornis (generally called just morrel or red morrel), Eucalyptus melanoxylon (generally called black morrel), and Eucalyptus oleosa (generally called just morrel or red morrel), and I have no idea which of them are represented on this page.
my samples: NOTE: these pics were all taken in very bright incandescent lighting ("soft white" at 2700K) colors will vary under other lighting conditions
burl listed as black morrel / Eucalyptus melanoxylon --- my guess is that this color is exaggerated quite a bit.
red morrel burl turning sticks all from the same vendor
moistened burl listed as red morrel
pen blanks, not listed as burl but clearly they are