Most tree species try to seal the edges of wounds by forming a callus layer.
In 1931 Callus resigned from all of his offices in Malta and permanently left for Hawkesyard, and then, a year later, for Oxford, England, where he stayed until his death.
A second probable manual phalanx exhibits a "low rounded projection resembling a callus." Ralph Molnar considered the occurrence of three pathologies in one individual to be "noteworthy".
The leaves of the plant sometimes have hardened, orange-pigmented callosities on the blades which are thought to be egg-mimics.