Drypetes caustica is a tree that can reach up to 20 meters tall with a pitted, pale greyish bark and dense, dark, dull green-yellow foliage. The leaves are elliptic, tapering towards the tip with yellowish veins. Its small flowers are on short stalks, solitary or in clusters usually on woody knots. The fruit is spherical to elliptic, orange-yellowish with brown dots and hairy.
This species is endemic to Mascarene and grouped in the family Putranjivaceae. It is mostly found in intermediate forests amongst native canopy trees. The dense branching and leaf arrangement makes it an ideal home and nest for endemic birds and endemic gecko.
The bois bleu or white plum wood is considered ‘Critically Endangered’ on the IUCN Red Listing 2017 (unpublished). It is very hard to find seedlings in the wild as the plants rarely produces flowers and fruits. The population size is declining due to habitat loss and the invasion of alien exotic species.
In the past the tree has been a source of good hard timber. Its mustard oil like make it of chemical interest and probably of value to man which presumably has reduced the population size.
The sap of the tree is of a blue colour, hence its common name.